You can create new colours from existing colours, for example changing the alpha channel of existing colours, explicity setting any of the h, s, l / r, g, or b values, or applying calculations to them:
hsl(from var(--your-css-variable) h s l / 80%) # set the alpha channel to 80%
hsl(from var(--your-css-variable) h 30% l) # set the saturation of the colour to 30%
rgb(from aliceblue r g calc(b + 50)) # sets the blue value of the aliceblue colour to the blue value + 50
Edit: I realise now that this is an elaboration of this!