The contrastcolour macro returns whichever of two given CSS colours is deemed to contrast best with another.

An example can be seen in the template tiddler for tag pills.

Parameters

target

The colour to contrast against (typically a background colour)

fallbackTarget

An alternative colour to contrast against. This is used when target is undefined or not a valid colour

colourA

The first of the two colours to choose between

colourB

The second of the two colours to choose between