This newest example of the situation I think might be more problematic for the baker. From the news story that was posted earlier in the thread, it made it sound like all the person wanted was for him to make a blue cake with a pink center, and he refused. It did not say anything about further decoration of the cake with pro trans wording or anything, just a blue cake with a pink center, which he refused to make after he found out that the buyer was trans.
This raises the question, then, does he refuse to bake ANY blue cake with a pink center? If the customer had not explicitly said that they intended to use this cake to celebrate their trans lifestyle, would he have still refused? If he wouldn't, if he only refused because he found out the customer was trans, then I can see him having legal issues over this one. Because then he's refusing to bake a cake that he otherwise would have, and that is more specifically prejudiced than just saying "I won't bake a cake that has pro gay wording on it" or whatever he said in the prior example.