Mixing of colors in an "objective" way like blur (lens focus) is a physical phenomenon, and should be done in linear color space.
Subjective things, like color similarity and perception of brightness should be evaluated in perceptual color spaces. This includes sRGB (it's not very good at it, but it's trying).
Gradients are weirdly in the middle. Smoothness and matching of colors are very subjective, but color interpolation is mathematically dubious in most perceptual color spaces, because √(avg(a+b)) ≠ avg(√(a) + √(b))
Subjective things, like color similarity and perception of brightness should be evaluated in perceptual color spaces. This includes sRGB (it's not very good at it, but it's trying).
Gradients are weirdly in the middle. Smoothness and matching of colors are very subjective, but color interpolation is mathematically dubious in most perceptual color spaces, because √(avg(a+b)) ≠ avg(√(a) + √(b))