The only difference the tape will make in the sound will be caused by how well the user can control and seal off the air flow around the tape. Generally speaking, however, the tape makes very little difference once someone learns how to use a mouth call.
As for the colors of tape, some folks use different colors for different call designs so they can quickly grab the call type they want without having to inspect the reed configuration. This is especially helpful under low-light conditions. Personally, when I am hunting, I carry several different mouth calls and know what sounds each of them will make the best in any given situation. I just look at the color of the tape and know which call I want to use for the set of circumstances I am in at the time.
