Ohhh amazing!!! Keep an eye on the shy one, I would hope it's not the case but if it's acting very different from the others it could be sick. Does it look smaller or skinnier than the others? Is it making stringy poop? Is it acting lethargic at all or resting on the plant? Hopefully it just feels like the odd one out if it's the only purple one and if you are able to get a few more of the same color it should hopefully perk up
You've gotten a few suggestions for plants and I would echo the recommendation for hornwort, it's a good option for a floating plant and can really provide cover for the tetras!
You should post pictures if you have a chance!