Contrast & Readability
Make sure all interactible objects and characters stand out from the background. Don’t rely on color alone -- use other principles of visual design, like line, shape, texture, and contrast. If you’re concerned about increased contrast harming the aesthetics of your game, simply add an assist mode that adds outlines or increases the contrast.
Adding assistive modes helps players who have issues with vision as well as new players who don't recognize interactable objects as easily.
Customizable Color Palettes
In an ideal game, players would be able to customize the colors of objects to suit their preferences. Colorblind players often struggle with multiplayer games that differentiate teams using color alone, especially when those colors are red and green (which is surprisingly common).
Alternate Color Palettes
When custom color palettes are too complex, provide alternate color schemes so players with colorblindness can tell friendly entities and harmful entities apart.
Alternatives to Color
If score is important to your game, make sure to double down and feedback and use audio to let the player know how they're doing, like ascending musical notes or louder sound effects when the player scores big combos, or using a voiceover to cheer them on.