So, to clarify, your suggestion is to have custom frac colors? Sounds kinda neat, but also super confusing for the opposing player. Adds the element of surprise to not being able to find out on what part you fracced your opponent.
If people with demo force behave like that in-game after agreeing to duel, they have no right for a refund. In fact, if they end up not sending the prize because of this, it's considered a duel scam. Report duel scammers. Having multiple frac colors wouldn't prevent this from happening.
But it would still be nice.