Doing these reminded me of some some color cards I made a while back, as suggested by Nita Leland in her book. I started off with the usual color schemes, complementary , triads, tetrads etc., and keep adding to them whenever I find something new. Notes can be written at the back, of the colors used etc. Its a useful and fun exercise, it makes you think of hue/value combinations and keeps your eye sensitive to colors outside. And of course, serve as references for future projects and paintings.
This is my delightful little ficus plant which had (then) just been repotted, too big for its old home, growing almost to the size of a small tree . I had sketched this in with a fountain pen, and I wanted to test if the ink was water soluble or waterproof and its turned out to be neither, just seems to be faded somewhat where I had added the water:
Whenever I am outside I am usually observing the angles and proportions and shapes of things around, so if I get 10 minutes, I jot them down quickly. Subtle color combinations and fleeting atmospheric conditions though are very difficult to capture because you never seem to have the the exact color and I can´t get them all in memory. Here are a few outdoors along with some gestures: