Mason jars a great for this, but be sure to have two jars. Like that you can use one for rinsing and another as your supply of clean water. It’s good to get into the habit of using a clean water jar so that your watercolor paints don’t get contaminated with other colors when...
In addition there are chrome dioxide green (fiery), umber and black (see below: Tips for beginners). In the literature - especially in the one that divides watercolor painting into "right" and "wrong" - there are some "rules" that you can follow or not. They are only mentioned here ...