you can (you have to generally) change the color every time in the Color Palletes (2) that pop up top-left when using any Drawing Tool in Roll20. The Default / initial color setting of those, should be 2=Transparent Fill.... 1= should match your Player swatch color choice, by your avatar, same as your 3D dice. For better or worse, the tool usually resets to your default of Player-Color + Transparent, the complaint I've seen more often is that it doesn't remember your last-selection of colors, but goes back to this default. What's it doing on yours?