Time and time again I’ve seen games make unnecessary decisions in color usage that outright prevented me from playing the game due to my colorblindness
Aerothorn, via Rock Paper Shotgun
We estimate that over half a million current Madden NFL users are colorblind
Karen Stevens, EA Tiburon
Colours are useful means of communicating with well established meanings. However they are lost on people who can’t distinguish between certain colours.
Difficulty perceiving red or green in particular is very common, affecting around 8-10% of males, making both green and red look a brownish green, and there are several other less common conditions that affect other colours – tritanopia, difficulty perceiving yellow, cataracts, which can add yellow, even achromatopsia, a very rare condition where you have no colour vision at all.
Wherever you can, use colour as a back-up for another means of communicating the information, such as text or a symbol, pattern or shape. This can be by default, with the extra reinforcement often benefiting all players, or via a setting. Some colours also appear darker than without colour deficiency (most commonly red) so check using a simulator for foreground/background contrast too. There are accurate free simulators available, and Unreal Engine has a built-in simulator.
For instances where this isn’t enough, e.g. online multiplayer where there’s no chance to recognise a symbol before you’re dead, allow elements of UI and gameplay that are dependent on colour to be customised. Palette tweaking is limited, the wider a palette you have the less effective it is, so always try to reduce colour reliance through additional signifiers first.
Free choice, for example being able to choose which colour each team should be, what color the crosshair should be and so on, is the most commonly requested solution, but offering presets schemes for the common types is also valuable. Again test those schemes with a simulator as the first port of call, if you design for the full 100% severity you’ll also have covered the varying other degrees. Also ideally check with colorblind gamers, there are likely to be some in your office, but don’t rely on that for validation, due to the range of types and severities.
Filters can be tempting, but they’re much more difficult to implement and are a blunt instrument, changing colors of elements that do not need to be changed, unnecessarily affecting aesthetics and introducing new clashes, and not allowing any way to reach edge cases.
Lastly, if you have a very limited colour reliance, for example only needing to distinguish two teams, it is possible to use a colourblind-friendly palette by default. Orange Vs blue works for the three most common three types, and if you add a contrast difference, e.g. light blue Vs dark orange, you can cover edge cases too.
Best practice example: Grand Theft Auto IV map (integrated use of symbols)
Best practice example: Puzzle Retreat (integrated symbol as well as colour)
Best practice example: Two Dots (option to add symbols)
Best practice example: Hue (option to add symbols)
Best practice example: FTL (option to add pattern and change colours)
Best practice example: Destiny (preset palettes for different common types)
Best practice example: Battleborn (freely customisable team colors)