Are they vinyl tire or plastic ones?
In styrene I'd be sore tempted to use a pale sky gray as te undercoat for the whitewalls. Or maybe a medium blue for the more 'modern' less-wite whitewalls we see today.
For vinyl--dunno, probably depends on te vinyl used, and ow flexible.
Checking Scalemates, there's a review of the T1 and (in German) calls the kit tires "rubber."
Luckily, you get a spare tire upon wic to pratice (since you can stow it "good side out" to need.
Shoot, just noticed they make a Karman Ghia. Dang it. Owned an Alpine T1 at 17, and a KG at 18 . . . could get spendy. Sigh.