Is your feature request related to a problem? Please describe.
True custom data-driven biomes have been added in 1.16.2, utilized by a few plugins and datapacks. These biomes displayed on Bluemap get their custom tints replaced with a default green (Probably plains)

Describe the solution you'd like
Colors from custom biomes should be displayed properly in the render

Custom biome data is stored in datapacks

If it's difficult to obtain the biome data from the datapacks, then a temporary solution could be to allow users to manually specify the biome data through the world config.

I found this can be used as a temporary solution: https://github.com/StrangeOne101/Datapack-Bluemap-Generator

Implemented in 2.0

A precondition to implement this is that this custom biome-info is somehow saved with the world. E.g. in the level.dat or within the chunk-files itself.

A precondition to implement this is that this custom biome-info is somehow saved with the world. E.g. in the level.dat or within the chunk-files itself.

Biome id mapping is stored in level.dat
Biome borders are stored in chunk data
Custom biome data is stored in datapacks