Simple studies offer the artist a perfect chance to clarify intent... learn how composition, value, mass shapes, and color mixing are all interconnected.
This video shows detailed color mixing as per student's request. Murky color, mixing, applying layers of color are included. Although green is the target color to mix, we also look at how to mix supporting colors for green (such as the pale sky and the water) based on my plein air watercolor study.
Play with a photo or concept you like. Don't assume the photo has the answers. Often I put away the reference photo until after I've tried a few studies. Then I know which pieces of information to look for in the photo as selective info instead of copying every detail.
This exercises can be done in watercolor or gouache. For transparent watercolor instead of white use more water to dilute the color value (to make it lighter).