Q1: Why does blue and yellow light make white instead of green?
A1: Blue and yellow light mix additively. Yellow light activates both the red and green cone receptors in your eyes, while blue light activates the blue cone receptors. When all three cone types (red, green, and blue) are stimulated simultaneously with equal intensity, your brain perceives the composite signal as white light.
Q2: Why did my mixed blue and yellow paint turn a muddy brownish-gray?
A2: This occurs when one or both pigments contain a warm red undertone. A warm blue (like Ultramarine) or a warm yellow (like Indian Yellow) introduces red wavelengths into the mix. Because red, yellow, and blue together absorb nearly the entire visible spectrum, the mixture absorbs too much light and collapses into a dull, neutralized sludge.
Q3: Is blue truly a primary color?
A3: Blue is a true primary color only in additive systems, such as digital monitors and stage illumination (RGB). In subtractive systems like paint and printing inks, the true primary color is cyan. Calling blue a primary pigment is a historical holdover from traditional art education that predates modern optical physics.
