>>381
g1 = Plot3D[x^2 + y^2, {x, -2, 6}, {y, -2, 6},
       ColorFunction->(RGBColor[0, 1, #] &), DisplayFunction->Identity];
g2 = Plot3D[4(x-2) + 4(y-2) + 8, {x, -2, 6}, {y, -2, 6},
       ColorFunction->(RGBColor[1, #, 0] &), DisplayFunction->Identity];
Show[g1, g2, DisplayFunction->$DisplayFunction];