Short answer
Make sure the colours that must be told apart differ in lightness, not just hue, because greyscale keeps only lightness. Order series from light to dark in a meaningful way, add direct labels or patterns for anything that falls within a few lightness units of its neighbour, and remember that office printing and photocopying compress the light and dark ends further than the screen suggests.
Converting to grey discards hue and chroma and keeps an approximation of luminance. Two colours of equal luminance — a mid red and a mid green, or the Okabe–Ito orange and sky blue — become the same grey regardless of how different they look in colour. The table converts the Okabe–Ito palette to relative-luminance greys and sorts them. Seven colours spread across less than half of the available lightness range, with several neighbours only a few L* units apart. That is typical: palettes designed for hue separation are rarely designed for lightness separation, which is why ColorBrewer offers separate 'print friendly' and 'photocopy safe' filters in addition to 'colour-blind safe'.
An on-screen greyscale preview shows the best case. Real office printing adds dot gain, which darkens mid-tones and pushes neighbouring dark colours together; toner-saving modes lighten everything and can drop pale colours to paper white; and photocopying a printed chart typically loses the lightest and darkest steps. A useful working assumption is that two greys closer than about 10 L* units on screen may be indistinguishable after a mono print, and pale tints under about L* 90 may vanish. Sequential scales suffer most at their ends, which is why ColorBrewer flags which schemes remain readable after photocopying. Printing a test page on the actual office printer is more informative than any preview.
Where colours cannot be made to differ enough in lightness — more than about five categories, or a fixed brand palette — add a second encoding. Hatching and dot patterns distinguish areas in bar, pie and map charts and survive any printer; keep them coarse enough not to shimmer and fine enough not to dominate. Marker shapes do the same for scatter plots and line styles for line charts. Direct labels are the most reliable of all, since they make the chart readable even if the colour or pattern is lost. For stacked bars and pies, white separators between segments help the eye find boundaries between two similar greys.
If a chart is likely to be printed in black and white — academic papers, exam material, reports that are photocopied — design from lightness first. Choose four or five target lightness levels spaced at least 15–20 L* units apart, assign categories to them in an order that makes sense (for example, the most important series darkest), and only then choose hues at those lightness levels. The result still looks like a colour palette on screen but degrades to a readable set of greys. Sequential ramps are naturally print-safe as long as they span a wide lightness range; diverging ramps are not, because their two arms are designed to share lightness at equal distances from the centre, so a signed label or pattern is needed on one arm.
| Colour | Grey equivalent | CIELAB L* | Gap to nearest neighbour in L* |
|---|---|---|---|
| Yellow #F0E442 | #E0E0E0 | 89.2 | 18.5 |
| Orange #E69F00 | #ADADAD | 70.7 | 0.7 |
| Sky blue #56B4E9 | #ABABAB | 70.0 | 0.7 |
| Reddish purple #CC79A7 | #939393 | 60.9 | 3.1 |
| Bluish green #009E73 | #8B8B8B | 57.9 | 3.1 |
| Vermilion #D55E00 | #828282 | 54.4 | 3.5 |
| Blue #0072B2 | #6D6D6D | 46.0 | 8.3 |
Why: Their colours have nearly equal luminance.
Fix: Change one colour's lightness, or add a hatch pattern or direct label.
Why: Copying drops very light tints to paper white.
Fix: Start sequential ramps darker, or outline the areas.
Why: The two arms are matched in lightness by design.
Fix: Add signed labels or a pattern to one arm.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
ConventionStrong evidence
ColorBrewer lets users filter schemes as colour-blind safe, print friendly and photocopy safe, treating these as separate properties of a colour scheme.
Colourwise analysisStrong evidence
Converted to relative-luminance grey, the seven Okabe–Ito colours span less than half of the lightness range, and several neighbours sit within a few CIELAB L* units of each other.
Based on: Computed by Colourwise using relative-luminance greyscale and CIELAB L*; see the table.
Source: Color Universal Design (CUD) — How to make figures and presentations that are friendly to colorblind people; CIE (International Commission on Illumination) publications
FactStrong evidence
Crameri, Shephard and Heron include readability when reproduced in black and white among the properties of a scientific colour map.
Colourwise interpretationLimited evidence
A gap of about 10 CIELAB L* units between on-screen greys is a reasonable minimum to expect them to stay distinct after typical office mono printing.
Based on: Colourwise's working rule, reflecting that dot gain, toner saving and copying compress tonal range; not a measured tolerance for any particular printer.
Caveat: Printers differ greatly; a test print is the only reliable check.
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.