Warming or cooling a colour means rotating its hue slightly toward the warm (red/orange/yellow) or cool (blue/green/purple) part of the colour wheel, without necessarily changing its lightness or saturation much.
Practical advice
Adjust My Colour's 'warmer' and 'cooler' options do exactly this, and show the result at three strengths so a subtle or more pronounced shift can be compared directly.
| Hue turned by | Result | Hue | Reads as | ΔE00 from start |
|---|---|---|---|---|
| 30° towards yellow (warmer) | #B0A87E | 99° | yellow | 9.4 |
| 15° towards yellow (warmer) | #A6AC82 | 114° | yellow | 4.3 |
| Sage green | #9CAF88 | 129° | green | 0.0 |
| 15° towards blue (cooler) | #92B190 | 143° | green | 4.0 |
| 30° towards blue (cooler) | #88B39A | 159° | green | 8.0 |
A 15° turn towards yellow moves sage ΔE00 4.3: visibly warmer beside the original, and still a sage. At 30° it is ΔE00 9.4 away and leans yellow; 30° the other way gives #88B39A, ΔE00 8.0. A low-chroma colour like this one moves less per degree than a vivid one would.
How this was calculated. The OKLCH hue angle is rotated while lightness and chroma are held. 'Warmer' and 'cooler' are conventions about hue, not temperatures: for a green, warmer means towards yellow and cooler towards blue.