I don't know WHY did author added this, but without some "fixes" you can't add horns genes, hair color genes and maybe some other. If you want to "FIX" this, then you need edit THIS:

<raceRestriction>
<blackEndoCategories>
<li>BodyType</li>
<li>Head</li>
<li>HairColor</li>
<li>Jaw</li>
<li>Melanin</li>
</blackEndoCategories>
<blackGeneTags>
<li>BodyType</li>
<li>Head</li>
<li>HairColor</li>
<li>Jaw</li>
<li>Fur</li>
</blackGeneTags>
</raceRestriction>

To THIS (* - edited lines):

<raceRestriction>
<blackEndoCategories>
*<!--<li>BodyType</li>
<li>Head</li>
<li>HairColor</li>
<li>Jaw</li>
*<li>Melanin</li>-->
</blackEndoCategories>
<blackGeneTags>
*<!--<li>BodyType</li>
<li>Head</li>
<li>HairColor</li>
<li>Jaw</li>
*<li>Fur</li>-->
</blackGeneTags>
</raceRestriction>

Yes, you just need to add <!-- --> to remove red errors. Why <!-- -->? Because if you want, you can easily return original back by just removing <!-- -->

R-MK, PLEASE, REMOVE THESE RESTRICTIONS! >.<