What is a complementary color?

It's the hue directly opposite your base color on the color wheel, found by adding 180 degrees to the base hue while keeping saturation and lightness the same.

Why use complementary colors?

Complementary pairs create strong visual contrast, which is why they're a common choice for call-to-action buttons, accent colors, and high-impact design elements.

Does the output include hex codes?

Yes, the tool returns both swatch colors as 6-digit hex strings alongside the downloadable PNG, in the same left-to-right order as they appear in the image.

What if I enter an invalid color?

The tool validates the input as a proper 6-digit hex color (with or without a leading #) and shows a clear error message if it can't be parsed.

Complementary Color Palette Generator

Overview

Introduction

This tool builds a simple two-swatch complementary color palette from any hex color you provide, entirely with client-side HSL math.

It's a fast way to find a high-contrast accent color for a base you've already chosen.

What Is Complementary Color Palette Generator?

A generator that parses a hex color into HSL, computes its 180-degree hue complement, and renders both colors as equal-sized square swatches side by side in a single downloadable PNG.

It also returns both colors as hex strings so you can copy them directly into a design tool or stylesheet.

How Complementary Color Palette Generator Works

The base hex color is converted to red/green/blue channels, then to hue/saturation/lightness. The complement's hue is the base hue plus 180 degrees, wrapped into the 0-360 range, with saturation and lightness left unchanged.

Both HSL colors are converted back to RGB and painted as 96x96 pixel blocks into a single PixelBuffer, producing a 192x96 output image.

When To Use Complementary Color Palette Generator

Use it when you've settled on a primary brand or UI color and need a strong contrasting accent for buttons, highlights, or calls to action.

It's also useful for quickly visualizing what a color's true complement looks like, since eyeballing complements is notoriously unreliable.

Often used alongside Triadic Color Palette Generator, Analogous Color Palette Generator and Color Wheel Generator.

Features

Advantages

Uses exact HSL hue-rotation math rather than an approximate color-picker guess.
Outputs both a visual PNG swatch strip and precise hex codes in one step.
Runs entirely in the browser with no server round-trip.

Limitations

Only produces the two-color complementary scheme; for wider palettes, use the triadic, tetradic, or analogous generators instead.
Does not adjust for perceptual color differences (like CIELAB); it uses the standard, widely-supported HSL model.

Examples

Red and its complement

Input

#FF0000

Output

A red swatch (#FF0000) beside a cyan swatch (#00FFFF)

Pure red sits at hue 0; adding 180 degrees lands exactly on cyan, hue 180.

A muted blue and its complement

Input

#3366CC

Output

A blue swatch beside a warm orange-ish swatch at the same saturation and lightness

The complement keeps the same saturation/lightness as the base, so both swatches read as equally vivid.

Best Practices & Notes

Best Practices

Use the base color for large areas of your design and the complement sparingly for accents, since two full-saturation complementary colors together can be visually harsh.
Copy the returned hex codes directly rather than eyeballing them off the PNG to avoid rounding drift.

Developer Notes

The hue/saturation/lightness conversions and swatch rasterization are pure functions operating on a plain Uint8ClampedArray PixelBuffer, with no DOM dependency, so the whole palette computation is unit-testable in Node.