Hi Steve,
I have to say I was hoping for these to show more marbling by now, I have had one or two over the years that showed poor marbling even at adult size but these are both very dark base colour, as I remember we picked this pair because of the light base....bizarre! What are your parameters? is the bottom of the tank mainly black? I have just got one back from an earlier batch at work, this ray is 12" disc and looks magnificent apart from the fact it was born with a deformed tail which needed amputation, we call it stumpy. If my memory serves me right the small Marble you part exchanged for these two was extremely dark also when you brought it back (not one of mine). These are still small and its quite possible they could be late developers. Keep me\us updated with any progress, if they don't make the grade then I will sort you something out Steve, swap them with another pair or something, I want you to be happy. Lets give them a while longer yet, its still early days.
The male has great spotting, we need some marbling thrown in there with it though.