Hmm.. My Mata was very blue in the body.. And it only developed the yellow as it matured and obtained it's streamers.. But it looked exactly like that in its transition stage(at maybe 5 to 6 inches). But as it fully matured, more and more of the yellow beauty came out.
It is difficult to say, but Google the Mata and other surgeons.. I think Mata that you are speaking of may be a little off color, as I have seen a few that were indeed purple tinted in their color also.. But the picture looks just like mine.. Exactly like him..
From note 5.. rip note 7