Tool
What the Complementary Color Finder does
Complementary Color Finder: calculates Palette (HEX) from Base colour.
With Base colour entered, the Complementary Color Finder works out Palette (HEX). Everything recomputes live, which makes it easy to test a few scenarios in a row.
Picking colours that work together is easier with the maths already done. The Complementary Color Finder exists to take that particular chore off your hands.
Your data stays on your machine. Once the page has loaded you could disconnect entirely and it would still work.
Field definitions, the method, and a worked example from the default values are all set out further down the page.
What do the Complementary Color Finder fields mean?
The Complementary Color Finder uses 1 input. It opens with a complete example loaded, which is usually the quickest way to understand what a field means.
| Field | What to enter | Default |
|---|---|---|
| Base colour | optional | #2563eb |
How does the Complementary Color Finder work?
Each output is derived from the inputs above in a single pass; there is no hidden state carried between runs, so the same inputs always give the same calculation.
Validation runs before the calculation, which is why a mistyped value shows an error rather than a plausible-looking result.
What a typical run looks like
You provide: Base colour
What happens: the file is read into memory by your browser, processed locally, and offered back as a download. It is never uploaded.
You get back: the finished file to download, with a line in the panel saying what was done.
Because the work is local, speed depends on your device rather than our servers, and large files are limited only by available memory.
Complementary pairs
Complementary colours sit opposite each other on the colour wheel: 180° apart in HSL hue. It is the highest-contrast pairing available, which makes it powerful and easy to overuse.
| Rule | hue + 180° | blue 220° → orange 40° |
|---|---|---|
| Contrast | maximum | strongest possible hue separation |
| Typical use | accent against a dominant colour | call-to-action against a brand base |
Worth knowing
- Complementary pairs at full saturation vibrate uncomfortably where they meet. Desaturate one side, or separate them with neutral space.
- The usual ratio is roughly 90:10, one colour dominates and the complement appears only as an accent.
- High hue contrast is not the same as high luminance contrast. A complementary pair can still fail WCAG for text.
Read next: Colour Contrast and WCAG: The Ratio, the Thresholds, What They Miss
How to use it
- Type Base colour.
- The results panel stays in sync with the form as you edit it.
- Look at Palette (HEX) in the output panel.
- To keep the result, either copy the link or print the page. Both preserve what is on screen.
What this tool does not do
- Colours render differently across displays; the values are exact but the appearance is not guaranteed.
- Conversions between colour spaces with different gamuts are approximate at the edges.
- Treat it as a fast first pass, not as the final word on a decision that matters.
Frequently asked questions
Base colour. That is the whole form. Defaults are loaded for all of them, so nothing is mandatory before you see a result.
No: there is no server involved. Close the tab and the values are gone.
It is free with no conditions: no sign-up, and no limit on how often you use it.
It follows the standard definition for this operation, so the result matches what a reference implementation would give.