I hear black makes them darker but it makes their whole body darker so it doesn't help with the contrast, right now I have a black back ground with tan pool filter sand, do u think that will help their colors look good? I'm picking 1 up tomorrow
honestly i would go with black. I have Tan in my tank right now and it looks good don't get me wrong but your ornate will get darker and with some plants or objects get some green thats why i'm gonna change to black sooner or later. So IMO i would choose black but if you don't want to i don't think it's a decision to loose sleep over.
I have black in my tank with my ornate. It seems to keep his blacks nice and dark and the yellows seem vibrant in comparison. I haven't noticed any overall darkening of more black than black and yellow compared to what I had before, just the dark parts are darker. He's 3.5 years old now and still looks great colour and contrast wise.
p.s. I also hear dark red or even pink (believe it or not) is a good colour to go with as well to show their more natural pattern colours.