Question 1

Why does shadcn want HSL?

Accepted Answer

Because the variable holds just the channels (e.g. 239 84% 67%), the same value can produce a translucent variant via hsl(var(--brand) / 0.5). You can't do that with HEX.

Question 2

Why does raising HSL lightness sometimes look washed out?

Accepted Answer

HSL isn't perceptual: the same lightness looks bright in yellow and dark in blue. When building a scale, targeting perceived brightness instead of lightness gives consistent results — that's what the brand kit tool does.

Color Converter