Implement dynamic colors for boot animation.

This CL won't cause any visual change to the boot animation yet
because the asset zips are yet to be udated.

Next steps:
- Update format.md to include documentation for dynamic coloring.
- Update asset zip files.

Test: Manual
Bug: 190093578

Change-Id: I63fdb1983896f321288d595d06f46bcde7da1aab