Are you afraid of how your future boyfriend will react?
Hmm... considering the location of your hemangioma, I think that when the guy sees it for the first time, he'll be so excited that he will barely notice it. In fact, if you had a third arm attached to your stomach, he would propably not have noticed that either
I thought a lot about that when I first met my boyfriend. Afterwards, I felt really stupid because I tormented myself with such silly thoughts. Even though half of my body is red/purple, he didn't think it was such a big deal. He just was the happiest man in the universe the first time he saw me naked
If you want to bring it up in a conversation, a way to do it is to say "Wanna see something strange?" and then just show it. If he is worth keeping, he won't react negatively. He'll propably just show you something weird on his body, like his jelly toe that can bend in all directions, his ability to fart with is armpit or some other "party trick".
Good luck to you! *hug*