Rounds don't work best for enhancing the color of a stone. Colored diamonds may be cut for color retention vs light performance. The busier facets that radiants have help to amplify the color in colored diamonds due to how the light travels through the diamond. David at Diamonds by Lauren would be a good person to explain all this to you. I'm just paraphrasing. I'd just have someone like that help educate you on colored diamond basics. There are different things to look for.
Diamonds by Lauren is a pretty cool site with lovely pieces at reasonable prices, but the color of their fancy yellows are all too light for me - the fancy yellows at Tiffany seem more like the fancy intense colors advertised on the DbL site. I'll take a look at the other site you linked me Thanks!