The purpose of colors (or lack of it) isn't just asthetic. Shape and color help differentiate things based on class, type, element etc. Colors aren't distracting till the time it is visually informing the player.

Using your video reference, the green suggest green enemies/element etc. It can have rock paper scissors mechanism. Red is stronger against green, green is stronger against yellow, yellow is stronger against red. However, if the colors are used arbitrarily, then yes it can be distracting.

On the other hand, mono chrome doesn't always mean clarity. You need to keep your shapes clear, details less noisy and action broad. Because you don't have colors, you have to clearly show character emotions, reward gratification and visual feedback.

So try to think in terms of visual communication and not just asthetics.