png-palette metadata and support for multiple palettes

[dazza-codes]

For raster mbtiles, it could be useful to store pixel data in greyscale and apply colors through a palette. It could be more useful to have an option to select or join a palette with pixel data for any given tile query.

1. What storage and/or query support currently exists for palette colors on raster mbtiles?
2. How could the palette be updated?
3. Could metadata support N-palettes?
4. How could a palette be selected or joined during a query?