@Wolphawkien
If your product icon or any pictures you used for the products page show hips touching between two people, IMVU considers that a picture of possible penetration and will disable a product for it. They take into account images and keywords used in the product name / description, not just the product its self.
IMVU also has a size limit on limp dicks. They're not allowed to be over a certain width nor hang beneath a certain part of the legs. It's possible that turning the dick black made it look larger to them. Or, you might have used a smaller than normal avatar in your product images, thus making the dick look larger in comparison ... hanging beneath what they consider the acceptable point on the legs.