Colormap in plot.contourf leads to single colored plot

If you select the colour map in plot.contourf(), the diagram is coloured uniformly with one color. Still the colorbar on the side shows a differnt colorsheme, maybe that is why it is single colored? The plot only shows one color since it is not in the colorbar defined?

Example:

fig = ogs.plot.contourf(
        mesh_slice,
        concentration,
        cmap="PuOr"
    )

The current workaround is to define the colour palette in the variable, which I find unintuitive.