Label translation/independent definition

[strarsis]

• [x] I've read the guidelines for Contributing to Roots Projects
• [x] This request isn't a duplicate of an existing request
• [x] This is not a personal support request that should be posted on the Roots Discourse community

Summary

Currently color labels can't be translated using the WordPress i18n functions (like __). Also it may make sense to be able to define a different label/slug.

Motivation

Multilingual backend language should support translation of Gutenberg colors. The slug stays the same, but the labels are different.

[Log1x]

This will require making a php export mode.

[strarsis]

Revisting this issue: Such a feature would be awesome as it completely avoids code/style deduplication.