Use the wheel to explore hue
Start with a hex, RGB, or HSL color. The picker rotates its HSL hue while keeping saturation and lightness. Complementary rotates 180°, analogous uses ±30°, triadic uses 120° intervals, split complementary uses 150° and 210°, and square tetradic uses 90° intervals.
The wheel markers show the chosen hues; the swatches show the actual resulting colors. For a pure red base, the complementary hue is cyan. That pair has roughly 3.19:1 contrast: enough for large text under WCAG AA, but below the 4.5:1 requirement for normal text.
Check the pair that carries meaning
The tool compares every pair using sRGB relative luminance. It does not round a failing ratio upward before deciding pass or fail. W3C explains the 4.5:1 and 3:1 thresholds.
Copy the colors as hex values, RGB values, or CSS custom properties. The onward link carries colors 1 and 2 into the color converter for more detail. Real page backgrounds, opacity, gradients, and text sizing still need checking in the finished design.