You don't have room for much in your 10. Going by your own self-described 2"/gallon rule (???), you already have 10" of fish and a snail (dunno how you count that one) currently.
If anything, the platies would be your best bet and they come in a variety of colors - red, orange, yellow, blue, then the various patterns as well.
While there are plenty of people who mix the two species, guppies would not tend to do well with danios -- especially the males considering there are only 4 danios. (the fewer the danios, the greater the likelyhood of nipping)
Swords and mollies really aren't 10 gallon fish. But, imo, neither are danios.