From rough to smooth

so, my drawing process is that i first do the sketch with a really thin brush, i might not always say it, but honestly i think sometimes i just like to sketch rather than color the drawings.
however after that i figure out proper shapes and which to color with what color and then use a hard round or hard edge brush to place different colors.
then i blend the colors together.
this part is a bit hard, because if i am not carefull the drawing can turn into mud color