Wrong results of combining oceancolor and landcolor

[zxdawn]

Description

When the oceancolor is combined with landcolor, only the ocean is shown.

Steps to reproduce

import proplot as pplt

fig, axs = pplt.subplots(proj='npstere')

axs.format(boundinglat=60, ocean=True, oceancolor='blue1', land=True, landcolor='gray5')

Expected behavior:
Like combing facecolor with landcolor:

import proplot as pplt

fig, axs = pplt.subplots(proj='npstere')

axs.format(boundinglat=60, facecolor='blue1', land=True, landcolor='gray5')

Actual behavior:

Proplot version

3.5.1
0.9.5.post202