Even without knowing more of the details, one has to admit that the case is a little odd. Valuation experts will always have price opinion differences, based on each individual valuator's prior experience, and risk appetite; however, a valuation difference of almost 33% is a little too big to be laid at the feet of differences in judgment without further explanation.
That being said, this is how one catches, and deals with, racism: find the actual perpetrator, develop a concrete case, and take them to court to face the music.
Unfortunately, I fear that this will simply end up resulting in another stupid class-action lawsuit against all Texas real property valuators, with racism presumed into the mix based on much smaller differences in valuation, and without the benefit of a fully independent valuation where the only salient difference is the apparent identity of the owner.