Mood Congruence
People generally like for their UIs to "understand them". They like for their interfaces to be in tune with the context around the task at hand. If you're accessing a banking app, you'll likely want a UI with minimal colors, high legibility, and very few distractions. But, if you're playing a game, you can likely find a lot more joy in a UI that is more colorful and playful.
This is the concept of "mood congruence". The UI should be in tune with the mood of the user.
Both examples below are functionally achieving the same banking task. See your balance, and move money as needed. The first window keeps the tone calm and legible so the interface matches the serious financial context. The second turns the saturation, motion, and promotional chrome way up, making it far less legible and usable as a utility tool.
Not actually sending any money.
Not actually sending any money.