correction : edit backlight color

[nitrateag]

Backlight color was unavailable for "Digital Rain" and "Typing Heatmap"

Description

"Digital Rain" and "Typing Heatmap" use a unique color. This color is alredy editable, but the control was missing.

Types of Changes

• [ ] Core
• [x] Bugfix
• [ ] New feature
• [ ] Enhancement/optimization
• [x] Keyboard (addition or update)
• [ ] Keymap/layout/userspace (addition or update)
• [ ] Documentation

Issues Fixed or Closed by This PR

• I didn't see any issue about that

Checklist

• [ ] My code follows the code style of this project: C, Python
• [x] I have read the PR Checklist document and have made the appropriate changes.
  • I didn't find the "develop" branch... sry, I'm probably dumb
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
  • This is a simple UI correction, no more test or documentation update are required.
• [x] I have tested the changes and verified that they work and don't break anything (as well as I can manage).