A misclick and one could mistakenly open fedora-dvm in place of whonix-dvm; Both the same color in applications menu. A experienced user could make this mistake, like having had a few drinks or when are sleepy and ignore clearnet usage. Avoiding accidental openings of the non-tor browser or normal Firefox, I suggest, for peace of mind to all Qubes users. Disabling clearnet access with exception the user wants to allow such action. (Please excuse if there is trouble understanding, I am from Russia and learning English.)
You can in principle give them different colors. Also, you can run them without the appliciation menu, but hitting alt+F3 and entering a few letters of an app (e.g. “torbr”).
See also: Pусский язык (Russian) - Qubes OS Forum.