Can't change fill color in shape nested in movie clip

I'm trying to change the fill color of shape/symbol nested within a movieclip but I can't get the code referenced in in similar post on this forum to work. 

this.myMC.mySymbol.shape_1.graphics._fill.style = "rgb(20,22,36)";0);

Throws an error. What am I doing wrong. What would be the proper way to change the fill color of a symbol/button or movieclip?