Artists work with their darks at different times of the painting process ... I find that 95% of the time with my watercolors I hold off until the finishing steps for place the darkest darks and make the lighter values POP!
I am preparing an assortment of items for an upcoming holiday bazaar in Bloomington IN and as I worked on these little snowpeople, I had to restrain from putting in the dark coal and brown twigs... I knew that would make it look so much better ... but in watercolor - it can/will smear!
Everything takes time in art and in life.... patience is often required to be "successful". Working (and playing) at your art every day brings about the knowledge to know when it is the time to control or let loose.
Enjoy the process!