Online courses are an amazing resource. I’ve watched little snippets to answer a question I had, or dipped into a series called “The Mind of Watercolor” (free on youtube), purchased courses from Will Kemp Art School (he’s adorable), and currently am doing a purchased course on brushstrokes. From Udemy. The teacher has a free youtube video series (3 parts) on brush strokes through history. Very complete, it seemed. Jill Poyerd is the instructor.
Tonight I watched the course videos on gradients (gradual transitions from light to dark) then played around with these guys, using white and yellow oxide oil paint.