What a complement really is
Convert the colour to HSL, add 180° to the hue, keep saturation and lightness untouched, convert back. Because only the hue moves, the two colours feel like they belong to the same family of intensity — a common failure of picking an accent by eye is grabbing something far more saturated, which then screams on the page.
Groups often move straight on to the colour picker afterwards.
Using complements without pain
A full-strength complement is loud. The usual rule is roughly 60/30/10: the base colour dominates, a neutral carries the middle, and the complement appears only on the thing you want clicked. If straight opposition feels harsh, the two split complements at 150° and 210° give the same tension with more room to breathe.
Triadic schemes at 120 degree spacing and tetradic schemes at 90 degree spacing follow the same logic if you need more than one accent.
Check it before you ship it
Complements are equally bright by construction, which is exactly why complementary text on a complementary background is often unreadable. Run any pairing through the contrast checker first, and use the palette generator if you want a full five-colour scheme rather than one accent.
The rotation is calculated in your browser and nothing you paste is uploaded. Aim for 4.5:1 at AA, or 7:1 at AAA, before putting one complement on top of the other.
Frequently asked questions
- What is the complement of #2942C6?
- An amber-gold sitting 180 degrees away on the hue wheel at the same saturation and lightness.
- Is the complement the same as inverting RGB?
- No. Inverting channels changes lightness too. A true complement rotates hue only.
- What are split complements?
- The two hues at 150 and 210 degrees from your base — softer than a direct opposite but still high contrast.
- Does grey have a complement?
- Not usefully. With zero saturation the hue rotation produces the same grey back.
- Is a complementary pair safe for colour-blind users?
- Often not — red and green complements are the classic pairing that red-green colour blindness collapses into one muddy tone. Blue and orange complements survive far better, and any pair should be backed up by a difference in lightness, shape or label.