everyone is correct,but incomplete.what you have to do(at least in my humble experience) is to start light and then go on darkening WITH the same yellow if you started with a very dilluted color(add more color to the misture until no more) upon the shades.if not, you have to SEE and understand the yellow this means where is pure yellow and where starts the shade and add, lets say raw sienna,to the shades,then the deeper the shade more raw sienna in to the mix.in both cases at the end you can add a misture, but very thinned or reduced mix of yellow with violet, in equal ratios.finally you can pass again just with violet at a very reduce ratio ALL over the painting.this helps to pop the color.in watercolor painting this is known as glazing.the most difficult thing to do is to start with a big block of one single color and then start to shade,lights and shades are worked from the very begining,so you can be able to "model" or "construct" the coloring,see where is needed more or to erase or leave it as it is.
sorry bro, in shading,no matter what it is (pencil,oils,acrylics etc)is no inmediate solution,you have to work it very slow.
hope this helps!!!and that i made my self understand.if you wish i can start a thread in color theory.