I found that corals that are yellow in colour, especially if they are of the bright lemon like yellow and not a yellow star polyp/or fiji toadstool yellow (mustard like yellow) and are the hardest to come by.... yellow hammers like that are rare and would cost you a bundle if you even are lucky enough to find one especially here in Canada.
http://reefbuilders.com/2013/01/08/n...hyllia-ancora/
http://reefbuilders.com/?s=yellow+hammer
msjboy