We only aim to support a whitelist of Less functions via our colour palette so in some cases this will be expected. Specifically we only support:
JavaScript:
(xf-diminish|xf-intensify|lighten|darken|fade)
Any additional functions that we would like to support in the colour palette JavaScript we have to specifically write the correct code to calculate that colour.
We're not against doing this, but it is currently working as designed so we'd have to consider it for inclusion in the future.