UM variables are not given correct color maps.

[jfrost-mo]

Describe the bug

UM variables are not finding the correct colorbar definitions, despite having their name translated.

How to reproduce

Steps to reproduce the behaviour:

1. Plot a spatial plot of a UM field (without a standard name)
2. Observe the colorbar is not fixed.

Expected behaviour

The STASH code is translated into a variable name, and that name is used to look up the colorbar to use, and that colorbar is used in the plot.

Environment

• Version: [e.g. from cset --version]
• Browser (if UI issue): [e.g. Chrome, Firefox]