$20s aren't purple. Period. Period..Struggling to see what the issue is here? You're murdering a fantasy chip so you can put a new denomination on it — so it can be used more efficiently in your game as... A fantasy chip?
Just not sure why you wouldn't use the actual $20 chip, or the $25 as-is, or relabel a different chip as a $20, just begging for confusion in games lol. Although maybe not outside CA...