If you get tank-bred rams, it shouldn't be that big of a deal. Steady parameters are better than constantly changing parameters. Unless you can find a way to soften the water that guarantees it's consistent (like mixing RO and tap to achieve a specific pH/hardness reading each time you do a water change), it's probably best just to stick to tap water. With rams, you're going to want to do at least weekly water changes to keep the nitrates/DOCs down.
I'm breeding electric blue rams and Bolivian rams in my tap water, which is about pH 7.6 and a TDS reading of 120ppm or so. No idea what that translates to in GH/KH. There are several breeders on AquaBid and SimplyDiscus breeding and raising rams in tap water with a pH in the 7s and moderate hardness.
How hard is the water?
Bolivian rams can take on a mottled black color. Usually when they're comfortable, they will lighten up and show their pastel colors. Both of my females showed a lot of black when I bought them, but after a few weeks it mostly went away. I only see it when they're stressed now.
Substrate and background color can also play a part in this. I notice that a lot of cichlids kept on dark backgrounds and substrate will show darker colors. I keep my rams over light silica sand with light blue tank backgrounds, so they tend to not show the darker coloration.
Watch them carefully -- if you have two unpaired fish, the dominant one is likely to coinue harassing the submissive one. This is why it's best to grow them out in groups where possible and wait for them to pair off on their own.