I see no reason why we can't use other full colors. The whole Redstone thing would just become a misnomer, something that is called one thing but doesn't necessarily mean it literally. Like how a pencil lead is no longer made of lead, blackboards aren't only black, etc.
Not liking an idea or wanting it to be changed because the name of something might not be 100% accurate afterwards is an incredibly bad reason. Plus if it was just darker and lighter shades of red it would be incredibly hard to determine wire strength because they would look too similar.