One of my favorite charts is my chart of brands and colors. I will write the name of the brand of watercolor paint at the top of the page. Then I will paint a swatch of each color and label them with a fade proof black pen. I will note if it is a transparent, opaque or semi-opaque color. Sometimes I will add the manufacturers notations as well, what grade the paint is, if it is fugitive and if it's a staining color. If I purchase a new color I make sure I add it to my brand chart. This is a great way to see the variety of colors you have tested and tried over the years.
In watercolor painting, it is good to really learn your palette. Study your colors. Create charts. You end up with a bunch of charts. A great way to keep track of all your charts is to put them into a 3 ring binder. I have created a bunch of my charts on 300 lb. watercolor paper because it's durable and my favorite paper weight to paint on. I make sure they'll fit within a 3 ring binder and then use a three hole punch on one side. Pop them into the binder and they're all stored in one place.