The Text Contrast Tool (CircularFLO Accessibility Tools > Text contrast check) and (GreenLight Eprdtcn Tools > Text contrast check) is a free tool to quickly check the amount of contrast on selected text and background colours.

Useful for print design as well as digital ebooks, the tool handles CMYK or RGB colours and tints and compares all selected text fill colours with all selected object fill colours.

Another useful free tool is