Sim Daltonism simulates color blind vision and displays the results in real-time in a floating palette. Freeware for macOS and iOS.
WhatColor for Windows and ColorCompass for macOS help color-impaired viewers identify and select colors.
eyePilot
Great for hard to read maps and diagrams. Floating, movable filter window helps color blind users by graying out non-target colors, flashing target colors, will identify selected colors by name, and cycle through a variety of image adjustments that change color and contrast. For macOS, Windows and iOS.
Visolve
The Visolve Deflector is a floating, moveable filter window that allows the user to lighten or darken problem colors. Includes unique "hatchure mode" useful for reading charts and maps. Will also filter entire screen using "toolbar" mode. macOS and Windows. Mac version includes a Dashboard widget.
Wikipedia is a good starting point for learning more about color blindness.
ColorBrewer is an easy-to-use online tool designed to help people select good color schemes for maps and other graphics.
The W3C provides a formula for determining whether two colors have sufficient color contrast.
