There are many colourful fish that would manage with angels. Neons tetras are not one of them; it is the angels' natural instinct to eat such fish, and even if they can't manage it yet, the neons can sense it. Aggressive fish (in this respect angels are aggressive) send out signals that other fish who are "prey" can sense, and that leads to stress and health problems. Best to avoid such things for the good of the fish.
Check out the fish profiles section; many of the characins are suitable, just notice the water parameter information as some of these are wild-caught and thus will not manage well in hard water; but the tank raised species and those that are naturally more adaptable will work. Species that work with angels are noted as such in the temperament section of the profiles. There are also livebearers, matching your harder water, and some of these are highly colourful. Mixing males and females will lead to copious fry which would be gobbled up by the angels, so bear that in mind; having only one sex eliminates that issue, though bear in mind that females can produce several batches of fry once they have first mated.
A Farlowella will not survive in hard water, unless you manage to find locally-raised fish and I can't say how long that might work anyway. These catfish are wild-caught in streams with very soft acidic water.
A comment on angels, they are shoaling fish that live together in groups; 4 or 5 in a 55g would work. They should also have plants and wood, branches, etc. They require security; their stripe pattern is a clue to the fact they they occur in water that has vertical camouflage, tree roots, branches, tall plants; and fish will always feel more secure and be less stressed in surroundings that provide what nature has programmed into their instinct. Filtration should be minimal, they occur in very slow or standing waters, and in very dim light.