Could be a color variant, could be a close conspecific, many possibilities. Many times isolation of species to a particular area allows for genetic specialization of coloration or physical traits that may not be seen in the rest of the species, and accounts for the drive behind Darwinian selection as we see specialization develop new species over time. A good example is to closely inspect Sailfin tangs from the Red Sea as opposed to those collected from the Indian Ocean compared to Hawaii. Differentiation has become so pronounced now that specimens from the Indian Ocean can be visibly differentiated from those collected from the Red Se, and there is now a complete specie difference in waters of Micronesia to Hawaii (check out Zebrasomas desjardinii vs. Z veliferum).
Keep in mind that there are many specimens of undescribed species of
Halichoeres and
Coris wrasses that still show up in aquarium shops, where identification may be based on the closest visual match of a specimen to the resources available in the LFS, and literally consists of the turning of the page.
FWIW, I do not think this is a
Halichoeres chrysis yellow wrasse, although it does resemble one, I think it more likely a
Coris spp. of some sort, although I don't recognize it. You might want to go to one of the ID sites like the one
Scott Michael supports t get a better ID. As far as the color changing being normal or not, yes, it is quite normal for specimens to become much more colorful once they start eating, establish a territory, and find a favorite sleeping spot in a new system.
HTH
