It looks like he still has some oil on the feathers. Or maybe the Dawn didn't get completely rinsed out - it's hard to get soap out of feathers. Don't wash him with any more soap, but you can give him a mist bath or a bowl of water to bathe in, whichever one he prefers. This may help get the feathers clean, or he may eventually preen the gunk out. If not then the problem will be solved when he molts.