Having worked in radio and dealt with many a promo pack I'd say keep it as simple as possible.
Bear in mind that the person who gets your pack will have hundreds of others. A fancy-schmancy one might get his attention, but in the end, it's the music that he has to be sold on.
I'd say colour of your choice, but nothing too bright or gaudy. Put it in a standard mailing envelope, even if you're dropping it off personally. The reason for this is that you want to put the specific person's name on there - that way they'll get to it first.
Hope this helps.
