I have been curious, not specifically with this set but in general, why the Tab is often/usually colored as a mod. It clearly isn't a mod and stylistically it seems it would look better if it matched the backslash, which definitely is an alpha.
https://en.wikipedia.org/wiki/Tab_key
Read the first line. Its definitely not a character tho it has its special charachter for text formats. It is an control (in term of moving text cursor or changing focus in user controls) key. Otherwise the enter/return is an charachter too since it has its special charachter "\r" or "\r\n".
I'm not sure how the first line explains why the tab key is normally colored with the mods, which generally aren't cursor control keys.
I wasn't saying tab is an alpha, but rather that it isn't a mod and I fully agree that it's closest to the return in usage.
Though, in thinking about this reply, I probably stumbled onto the answer...
I'd classify keys like this:
alphas = need no explanation but I would include spacebar since it's still a regular character
mods = keys that do nothing on their own and only modify other keys; shift, ctrl, alt, super
others = esc, tab, return, function keys, arrows, backspace/delete, home/end, page up/down
If you only have two "main" colors then you'd need to combine those three into two and it makes the most sense to color the mods and others the same.