I think people can have whatever kind of OC they want, whatever colour, whatever type of pony, whatever personality.... because not everyone can draw and everyone is on different creative levels and that is no-ones fault.
The only objection to OC's I have is if they are ridiculously over-powered... then it should matter. Because in an RP it affects your character more than anything else if their oc is.. I don't know, destroying the whole of Canterlot in seconds because they have the power to create rifts in space and suck everything in and banish them to an eternal land of darkness. But apart from that, no-one has the right to judge anyone's OC in terms of style, creativity and/or whatever else physical, because they are just owned characters, and it isn't like they are canon / going to be put in the show any time soon! The way an OC looks shouldn't matter to someone else. If they like it, great. If they don't, whatever.
We should all love and respect each others creativity limits.