I like basic colors. I have black gravel in my Tetra tank, with a small bag of orange gravel my 9 year old wanted and I wish wasn't there. I have "salt and pepper" cichlidsand in my multI tank that I love. And I have regular pea gravel in my 10 gallon, which looks good too.
I like more natural colors for larger tanks. I have brownish gravel in my 20 gal, mostly because I didn't want the other colors they had, and it was the only color in that size bag. But, in my betta tank, 2.5 gal, I had the neon gravel and neon plants and decor.
My tanks have the Red Fluorite in it so I don't really have gravel at all, but it does have a natural look to it. Noel's tank does have a little red gravel mixed in and it gives the Fluorite a rather neat look to it. I will say that the Fluorite does take a lot of washing to make it habitable for the fish and I mean a LOT of washing. (otherwise the water becomes quite muddy)
Bright colored gravel is stressful. That's like having walls painted bright pink or neon green...yikes! Some fish prefer darker gravel than others...tetras will show off their colors best with black gravel.