Additive Color Mixer (RGB Light Mixing)

Anyone who grew up mixing paint finds it odd the first time they hear that red plus green makes yellow. With light, though, that is exactly what happens: two spotlights aimed at the same wall add energy instead of removing it, which is how your phone screen, an RGB LED and a stage rig all work. This page lets you pick two colors and see the hex value their sum produces.

The math is plain: add channel by channel and clamp at 255. Red ff0000 plus green 00ff00 gives ffff00, the yellow you expect. The detail rarely mentioned is that the addition happens directly on sRGB values, which carry a gamma encoding, rather than on linear light. That is why two mid greys, 808080 plus 808080, come out as pure white ffffff when the physical answer sits closer to b0b0b0. Read the result as the teaching model, not photometry.

Use it to explain additive mixing, to reason about primaries and secondaries, and to predict what colored lamps do together. Do not use it to predict paint, glaze or print color, which work the other way round. Note the interface limits too: both inputs are native color pickers with no field for pasting a hex value, there is no ratio control between the two colors, and the result appears as text with no swatch. Everything is computed in your browser.