A handheld microphone can look unfinished on camera when its grille is exposed, particularly during an outdoor interview beside a stadium or training ground. A suitable cover helps reduce the effect of moving air and gives the presenter a consistent visual identifier.
It is not only a colour choice.
The microphone model, grille dimensions, foam construction, artwork method, cleaning routine and filming conditions all affect whether the cover works in practice. A neat appearance matters, but the cover must also stay in place, allow speech to remain clear and tolerate the way your production team handles equipment.