You find colored grasses in the fields around the Valley. Some color grasses, like Red and Orange and Yellow, you can only find in certain seasons of the year. There are only a few colors that you can find in the wild in any given season.
However, you can make curry with any color Grass, so you don't have to just make Finest Curry to raise his heart level. You can make a simple one-color curry, all of which he likes, except for Red Curry.
