The numbers describe the brightness, they can be useful if they're linked to UI usecases and if you're ok with limiting yourself to a prebuild color palette. It

The numbers describe the brightness, they can be useful if they're linked to UI usecases and if you're ok with limiting yourself to a prebuild color palette. It's just that functional names (btn-fg, btn-bg etc.) are better imo because they separate concerns. You could link them to a grayscale when prototyping and then later switch the colors in the stylesheet. It's also slower if you have to think about picking colors when coding.