Why limit anything. This is a game where we can (soon) be a male vampire Orsimer wearing a wedding dress, riding a guar, with a panther pet - is adding a blue dagger the point where it becomes ridiculous for you? Just because a we have the "possibility" to make a weird colored weapon doesnt mean the vast majority will. In fact, based on the looks of most people I see, i would bet the majority of bladed weapons will be grey, black, or red