As I explained to someone recently (I can't remember precisely where), the ceiling limit for happiness was raised hugely between gens 2 and 3. It's actually very easy to fix, but I can't remember where the byte is off the top of my head.
Thanks for replying, here's the tileset I've been working on:
So if my understanding is correct, I'd have to recolor these using colors from a palette in FireRed in order to insert these without any screwups?
If so, maybe I'll use Icefall Cave's colors.