What effect is generally produced by mixing all three primary paint colours?

Correct answer: Dark brown or muddy colour

When red, yellow, and blue paint are mixed, their pigments absorb different parts of the visible spectrum. Combining all three usually absorbs much of the light and produces a dark brown, greyish, or muddy result, making option D correct. Bright white belongs to additive mixing of light, not ordinary paint. Pure yellow is only one primary colour, and light pink would require white mixed with a suitable red or magenta.