The work you did with darks on wednesday involved more than value, and more than technique. Focusing on a challenging aspect of painting, even for half an hour, brings all the elements together. Making a smooth wash of a strong dark required being thoughtful about, and balancing, color choices, wetness control, and brush handling, as well as sensitivity to value.
If you already keep a notebook or a watercolor journal, great. if not, here's a good place to start. Articulating what you discover helps make it a permanent part of your repertoire.
Write down what you did to get your wash dark enough and reasonably even. Consider illustrating your notes, if you think it will help you imprint any new information. Where do you still need practice?
Do you think the same kinds of skills would apply to any saturated color, or are the issues peculiar to strong darks?
Make an abstract page of shapes, some of which are rich, deep washes of lighter colors, like cerulean blue, or new gamboge. Try a transparent color, like a quinacridone. And make some of the shapes velvety darks. We will discuss the differences and similarities.