He is registered black...
A black horse is black (of course) but a bay or brown horse is also black, just with another gene (agouti) to make the black only on the horses points.
So he could be DNA tested black (and he IS black based) E/_, and still be brown or bay (having one of the agouti genes with the black).
So unless you know he is actual black E/_ and NO agouti then he could still be DNA tested black, and have the black gene, but have other genes that combine to make him not black. Hope that makes sense, and sorry if you already knew that.
If you want to be positive you can send out another test for agouti to see if he is black, bay or brown (I think there is only one place that actually tests for brown).
Is it summer or winter there? I'm confused.