Color blending not working in non default color space

[Semigradsky]

color(yellow blend(blue 50% hsl))
//=> rgb(128, 128, 128)

this is blending in rgb color space. Should be rgb(0, 255, 128)

hsl(60, 100%, 50%) + hsl(240, 100%, 50%) => hsl(150, 100%, 50%) ^ yellow ------------- ^ blue