This is one of the many reasons why everyone should always have a spare trackball on hand.
The dye is permanent and will not come off. If it comes down to it, just return your old curve without any trackball in it. Tell them you wanted to keep your old TB as a spare.
I would take the track ball out of the new one when it comes and just keep your track ball that has the modification. Its not worth the risk if they do not honor your warranty because they will charge you regular price for the replacement. And it will be a refurb...you dont want to pay $400 bucks for a refurb....
a ball only cost $10 bucks so if you are really concerned its a cheap fix.