superimposing contour over geoshow with different colormap

Hello, I am using geoshow() with grayscale to plot Brightness temperature(BT) over Indian Region. But if I superimpose contour of BT geoshow, it does nothing. Is there anyway to plot geoshow and contour at the same time and with different colors. I have two datasets of BT. One I want to use with geoshow and other(with some eliminated values) with contour