So now the J-31 is painted in a darker grey and silver color? It must be another prototype I hope.
I think it is just artefacts of the photo, I dont' think there's concrete visual evidence of any change in paint scheme.
Certainly, if we're going by colour, I don't think it is the J-20 gray we've come to associate with 2011 and 2012 which are presumed to have RAM coating.
She's a good looking bird indeed. What the JSF could have been if not for the albatross known as the B version.