The mechanism is the same throughout; which axis of contrast is available differs by iris. A deep brown eye has almost no chroma for a complement to act on, so lightness does the work. An amber eye has more chroma than any other, so hue contrast is dramatic.
Dark brown eyes
A very deep iris with high melanin density, low measurable chroma and lightness close to the pupil. At conversational distance the iris and pupil often read as one dark shape.
The contrast available. Because the iris is so deep, hue contrast does almost nothing — there is not enough chroma in it for a complement to act on. Lightness contrast is what works instead: a light colour near the face raises the apparent depth of the eyes by comparison, which is the opposite of the advice usually given to lighter irises.
The mistake most often made. Being told to wear brown because it matches. Matching a deep iris with deep brown clothing removes every axis of contrast the eye had, which is the most reliable way to make dark eyes read as less distinct.
Brown eyes
A mid-depth warm iris with modest but genuine chroma, usually with visible structure and often with lighter flecks towards the outer ring.
The contrast available. Enough chroma for hue contrast to act on, unlike a very dark iris. Blues and cool greens sit roughly opposite the iris's orange-brown hue, which raises its apparent saturation. Lightness contrast works too, so this iris has both axes available.
The mistake most often made. Assuming brown eyes are the default that goes with everything and therefore need no thought. They have real chroma and a real hue, and they respond to contrast as much as any other iris.
Light brown eyes
A lighter, warmer iris where the golden and honey notes are visible in ordinary light rather than only in direct sun, and where the structure of the iris is clearly readable.
The contrast available. Higher lightness and more visible chroma than a mid brown, which means hue contrast works well and lightness contrast has to be handled more carefully — a very pale colour near the face can out-light the iris and flatten it.
The mistake most often made. Wearing very pale warm colours next to the face, which can be lighter than the iris itself and leave it looking flatter than it is.
Amber eyes
An unusually saturated warm iris — genuinely golden or coppery rather than brown, with the highest measurable chroma of any common eye colour.
The contrast available. This is the one iris with enough chroma that hue contrast is dramatic rather than subtle. Its complement sits in the blue-to-violet range, and the effect of putting one near the face is stronger than for any other eye colour in this set.
The mistake most often made. Treating amber as a variety of brown. It has substantially more chroma, and advice written for brown eyes systematically under-uses the contrast available.
Hazel eyes
A multi-toned iris carrying both warm brown or gold and green in the same eye, usually with the brown concentrated centrally and the green towards the outer ring.
The contrast available. The distinctive property is that a hazel iris does not have one hue — it has at least two, and whichever one is echoed by what is worn near the face becomes the one people notice. This is a genuine and repeatable effect, and it is what makes hazel the most responsive iris to clothing colour of any in this set.
The mistake most often made. Looking for the one colour that suits hazel eyes. There isn't one, because there isn't one hazel — the useful question is which of the two tones you would like people to notice.
Green-hazel eyes
A hazel iris where green dominates and the warm component is a limbal or central accent rather than half the eye.
The contrast available. Behaves much more like a green iris than like a brown one, but retains enough warm content that a warm colour near the face can still pull it towards hazel. The available contrast is red-through-violet, opposite the green.
The mistake most often made. Applying brown-eye advice because the record says hazel. A green-dominant hazel responds to the same contrast as a green iris, and warm-on-warm advice under-uses it.
Green eyes
A low-melanin iris where scattering plus a small amount of yellow pigment produces green. Chroma is genuinely modest — green eyes are far less saturated than photographs of them suggest.
The contrast available. The complement of green sits in the red-to-magenta range, and because the iris's own chroma is low, a moderately saturated opposing colour produces a large proportional change in how much the iris registers. Very saturated reds overshoot and simply become the thing you notice instead.
The mistake most often made. Wearing green to match. It is the most common instinct and the one that most reliably reduces how much a green iris registers, because it removes the contrast the effect depends on.
Grey-green eyes
A very low-chroma iris sitting between grey and green, whose apparent colour shifts more with surroundings and lighting than almost any other eye colour.
The contrast available. With so little chroma of its own, this iris is unusually suggestible: it takes on whatever hue is placed near it. That makes clothing colour more consequential here than for any saturated iris, and it means the honest framing is 'which direction do you want it pushed' rather than 'what suits it'.
The mistake most often made. Looking for a fixed answer. This iris genuinely changes with what is near it, so the useful decision is directional rather than definitive.
Grey eyes
A low-melanin iris where scattering produces a near-neutral appearance with very little measurable chroma — closer to a true neutral than any other eye colour.
The contrast available. There is almost no hue to emphasise, so hue contrast has little to act on. What does work is the reverse: placing a saturated colour near the face makes the iris take on a faint complementary cast by simultaneous contrast. A blue jumper can make grey eyes read blue, and it is a real perceptual effect rather than an illusion of enthusiasm.
The mistake most often made. Being told grey eyes are 'just' a pale blue and given blue-eye advice. A genuinely grey iris has less chroma than a blue one and responds differently — it takes on suggestion rather than being emphasised.
Blue-grey eyes
Between grey and blue, with slightly more chroma than a true grey iris and a clear cool bias. Reads bluer in bright daylight and greyer indoors.
The contrast available. Enough blue to be emphasised by warm contrast, and enough grey to be pushed by suggestion. Warm oranges and rusts sit opposite the blue component and do both at once.
The mistake most often made. Wearing blue on the reasoning that it matches, which reduces the contrast that would have made the blue in the iris more visible.
Light blue eyes
A very low-melanin iris where Rayleigh-type scattering dominates. Light in value and modest in chroma, with the iris structure — spokes, rings, crypts — clearly visible.
The contrast available. Two mechanisms are available and they pull in opposite directions. Warm colours opposite the blue raise its apparent saturation; deep cool colours raise its apparent lightness. A pale blue iris is unusual in being emphasised by both, and the two produce noticeably different results.
The mistake most often made. Assuming pale eyes need pale colours near them. A pale colour at the same lightness as the iris removes the contrast, and a deep one is usually the more striking choice.
Blue eyes
A mid-depth blue iris with moderate chroma, produced by scattering rather than by blue pigment — there is no blue pigment in a human eye.
The contrast available. The complement of blue sits in the orange-to-warm-brown range, which is fortunate: those are wardrobe neutrals in most climates. Rust, camel, tan and warm brown all raise the apparent saturation of a blue iris while doubling as things people already own.
The mistake most often made. Wearing blue to bring out blue eyes. It is the single most common piece of styling advice and it works against the mechanism — a matching hue lowers contrast rather than raising it.
Dark blue eyes
A deep blue iris with more stromal density than a light blue eye, giving lower lightness and a slightly greyer, more saturated appearance.
The contrast available. Deep enough that lightness contrast becomes useful alongside hue contrast. A warm mid-tone opposite the hue raises saturation; a light neutral raises the apparent depth. Unlike a pale blue iris, this one is not at risk of being out-lit by what is worn near it.
The mistake most often made. Treating it identically to a light blue iris. The depth changes which mechanism is available, and light-blue advice tends to under-use the lightness contrast this eye can carry.
Mixed or indeterminate eyes
An iris that does not settle into a single named category — often carrying two or more of blue, green, grey and amber in proportions that change with the light.
The contrast available. The same selection effect that governs hazel, applied more broadly: whichever hue is placed near the face becomes the one that reads. This is the most changeable category here, and the honest advice is directional rather than prescriptive.
The mistake most often made. Trying to find the category first. There may not be one, and the styling question — which direction to push it — can be answered without settling it.
Heterochromia
Two distinct colours present, either between the two eyes, in a sector of one iris, or as a ring around the pupil. The pattern matters more than the individual colours for styling purposes.
The contrast available. Standard contrast logic applies to each colour separately, which means the two can be worked against each other: emphasising one necessarily de-emphasises the other. The interesting choice here is whether to make the difference more visible or less, and both are reasonable.
The mistake most often made. Trying to make the two eyes match. They are not going to, and the styling decisions that work here are the ones that treat the difference as the feature.