Some people can not see the full colour pallet most humans can perceive because of this some colours become indistinguishable for them. There are also different versions of colour blindness so there are different people that can perceive the same different colours differently. There is a good overview of the general topic here:
Try to avoid colours that look the same for people with a form of colour blindness. This is a great page to be certain that a colour combinations works out: https://www.whocanuse.com/.
As an additional step, it is recommended to add a post-processing filter to a project that can change each primary colour to another or simply provide a number of presets.
While the inclusion of these filters is heavily recommended they can only do so much to improve how well colourblind people can see elements of the game. Ideally, the colour of each relevant object and the background it is placed on is selected with these limitations in mind and symbols and shapes are used in addition to colour to communicate relevant information (For example: It’s not the red keycard, it’s the red keycard with a star symbol). The filters will function as an additional support line for cases in which this is not possible for some reason.
Colour Recognition for Colourblind Players
Not every human experiences colours the same way, in fact most people see colours at least a little different. This is because the receptors in peoples eyes are slightly different. Different receptors can recognize different colours. People with colour blindness usually miss or have a weakend version of one or multiple types of receptors. Because of this ther are also multiple types of colour blindness.
Objective of Colour Correction Filters
The objective while catering for people with colour blindness is not to make the world look like it would for people without colour blindness, but instead is to make sure the differences between objects can be recognized.
Since colour blindness differs so much from person to person it is highly recommended to allow the players to create their own colour blindness filters this is done by offering sliders for each primary colour and allowing players to move them along a HUE value. The generated filter should adjust every inclusion of this colour to the new HUE value.
Makes sure that players have a few example screenshots when selecting their colours.
Additional Reading
https://midtownvision.com/blog-posts/types-color-blindness
https://personal.sron.nl/~pault/
Color Blindness and Creating Graphics: Some Examples and a Short Discussion
