Readability
Also said as Visual clarity, Legibility, Read
How quickly a player can tell what they are looking at and what it means for them: what can hurt me, what can I touch, where can I stand. Artists say a thing "reads" when it is understood in a glance.
When a game is hard to read, players get hit by things they never saw, and they blame the game, correctly. Beautiful detail that hides the enemy is a bug.
Say it
“Enemies and hazards have to read first. Drop the background to 40% contrast and desaturate it, keep full saturation for anything that can hurt the player, and give pickups their own colour.”
Where you’ve seen it
Cuphead colours the things you can parry pink, so in a screen full of bullets the ones you can slap are picked out at once.
Not to be confused with detail
Detail adds information everywhere. Readability ranks information, so the things that matter win. Adding detail usually makes it worse.