Kubotai rasboras are a very pretty green, and would nicely contrast the scarlet badis. I've found them to be easy keepers, and they don't harass my chilis or CPDs at all.
Actually, CPD's or the related "emerald tiger rasboras" (looks like a forest green CPD but with white stripes instead of white dots) could go well with the scarlet badis. Mine only chase eachother, and not with any real agression. Only issue with those is that they can be rather shy too.
I don't keep scarlet badis anymore, but I did in the past. They were ferocious with eachother (rather like little cichlids, actually), and definitely need small caves to feel secure, but they got along very well with the small tetras and baby cories they were kept with. The more cover they have in the tank, they more they feel safe to venture out, so heavy planting is a must. They actually did well in our local hard water, and I found them to be quite hardy once settled in (they are sort of susceptible to transport stress right upon purchase IME, but if they make it a week they are good to go). Mine took a while to get used to crushed flake & mini pellets, they preferred the frozen bbs and cyclops with a tiny bit of mini bloodworms (they didn't seem to mind that it wasn't live food as long as I dripped it down from above so it visibly moved through the water column). Don't over do the bloodworms though if that's part of your feeding schedule; I've heard they are prone to health issues if those comprise a large portion of their diet, so I tried to keep them to less than 10% of total intake. Once trained to eat commercial prepared foods, I fed about 50/50 prepared and frozen, and they conditioned & colored up nicely on that combination.