I think I’d only consider it dark if my card was going to be charged. If the app admitted it was just to verify that I’m a real person, for security reasons, I’d be fine with it.
The problem is you don't know if your card is going to be charged. It's too easy for companies to hide things in long terms of service click-throughs, or for users to misunderstand new services, or for companies to charge cards "by accident". I'm certainly pretty doubtful that I completely understand what I'm agreeing to with a new company. The simplest safest solution is to not give them your card.