The reason that you can't dyesub on black keys is best compared to being unable to see in pitch black darkness. The color/white may be there when you turn the light on, but it is overpowered by the darkness. The metaphorical turning the light on, is lightening the key color. Thus the better colors turn out on whiter keys, and the more contrast is shown.
Anyways I'm going to assume Boilermaker did mean that he wanted some of the function row set as doubleshots, but remove them from the set, creating either duplicates or replacements. Thus those that wanted a doubleshot companion cube Esc only could have that, and if someone wanted the whole function row, they could get the whole set... or if they wanted both they could use them interchangeably, since it would likely have the same legend. I don't think I will be removing 2 of the most popular legends from the full set, even if an equivalent doubleshot is offered standalone.
Anyways, I'll get an image up here soon where I circle the legends I'm considering dropping, and potential ones I'd like to replace them with. Ones like the guy falling in the water or getting hit in the face with the... whatever that ball of stuffs is, can go and in their place we get a potato and... whatever else you guys like!