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
Colours are useful means of communicating with well established meanings. However these meanings vary between countries and are lost on people who can’t distinguish between certain colours.
Red-green colour deficiency 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 forms that affect other colours.
Wherever you can, use colour as a back-up for another means of communicating the information, such as text or a symbol. For instances where this isn’t possible, ie. online multiplayer where there’s no chance to recognise a symbol before you’re dead, offer a choice of colour schemes, and test those schemes with a simulator (and also ideally colorblind gamers, there are likely to be some in your office). There are free simulators available, and Photoshop and Unreal Engine 4 both have built-in simulators.
Some colours also appear darker than without colour deficiency (most commonly red) so check for foreground/background contrast 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: Call of Duty – Black Ops 2 (separate mode for alternative colours, only works for limited palletes)
Best practice example: FTL (separate mode for alternative colours and use of pattern)
Best practice example: Sim City (separate mode for entire pallete shift, only works for limited palletes)