They are all pretty easy to germinate in my experience.

Given a bit of heat, they germinate in a few days. See this URL to get an idea of the varieties available (click on the pictures to enlarge).
http://www.raretrees.org/aman0219.html

Thank you both. The site was very helpfull.

I'm trying two types of amaranthus this year... the hopi red dye are sprouting just fine, but not one of the tricolor splendens have germinated so far. Frustrating.

That's strange - maybe it's dud seed? I ordered seed of A tricolor 'Early Splendor' from JL Parker 2 years ago. It was such a big pack that I've been using it each spring ever since. It certainly remains viable a long time - I just keep it in the fridge. This year it germinated just 2 days after sowing (in heat). This is a plant well worth growing.