The colour axis is an object of the type TPaletteAxis. Here the code i use to format it nicely:
def ScaleZAxis(histname): hist = ROOT.gDirectory.Get(histname) ROOT.gPad.Update() palette = hist.GetListOfFunctions().FindObject("palette") palette.SetX1NDC(0.90) palette.SetX2NDC(0.92) palette.Draw() ROOT.gPad.Update()