That's great news! Eating is always a good sign once they stopped.
I'm not sure if it's the new water, or the conditioner that helps more, but either way, I'm glad to hear it :) Mine did the same at first, but a couple water changes later (siphoning gently and quietly from the corner) they came around. Maybe it's partly the interaction, I have no idea. I'm just glad so far it's working out for us.
For the white platty, I'm not familiar with them outside of googling a few pics, and the few I did seemed to have red here and there, often in the face. How long have you had this one? From the sound of it, long enough where you know what it should look like...We have all seen fish loose color to shock when we bring them home, but usually it returns shortly after. Any chance the fish was stressed or in shock and is just now showing all it's colors?
Is it much more red than this?
Also check out near the gills and see if they look blood red and raw or anything crazy like that.