Here is a little resource that I really love. It takes the guesswork out of mixing your paint colors, and if you purchase the smaller one (as I have) the paint colors on the sides are probably tubes you already have on hand.
One side has the dominant color, the other has the mixing colors. Old friends like Burnt Sienna, Alizarin Crimson, Ultramarine Blue, Sap Green and Payne's Grey are all on this chart. I love how I can see a color, and choose it , knowing what combination of paints I need to create that color.
As well, the sheet is LAMINATED, making it paint-proof. Yay! for those of us who are "messy" painters!
So if you are in an art supplies store, or ordering online, you might just want to include this inexpensive but invaluable tool in your purchase. :-)