Of course there was also no rule saying that chess functioned on a restrictive rules system and a lot of evidence that it instead functioned on a permissive system. Which would invalidate the "no rule says I can't" argument.
(when designing a game's rules, "restrictive" means the approach is "everything is permitted by default, unless explicitly restricted", while "permissive" means "everything is forbidden by default unless explicitly permitted" -- if we assume that chess is a restrictive-rules game, we can similarly mate in one from almost any position by simply inventing new pieces with unusual abilities and declaring that "the rules don't say you can't!")
If the rule was simply, "A promoted pawn may be exchanged for any piece," then that would fit within a permissive system, and still qualify as "nothing says you have to promote to the same color."
No. It was unclear whether you could promote to a piece of the other colour, but a conforming implementation of chess will not make demons fly out of your nose.
