Hello!
You can find the color wheel by clicking on the single active color swatch in the upper left corner. Sometimes the color wheel window then hides partly (so you can't move it) or completely (you don't see it at all) "behind" the application. Then simply decrease the app window size (upper left corner, green button) and look behind the application. You can move the color wheel somewhere else on the screen in front of the app window from there and the problem should be solved until you restart the app. Same goes for the detailed brush window (you can fid it when you hit the brush pattern with the small number underneath right next to the active color swatch).
Hope this was helpful!