Previewing

The best way to preview what your mask is doing is to go into Material Mask Debug Tool by selecting it on the toolbar while in Biomes mode. There you can select for which species or sub-biomes you want the preview and for which mask.

This view always shows the state of the last generation. It doesn't start generation on its own.

With this tool selected starting generation updates only the Persistent State of the generation.

Which means a shorter generation time. But spawned assets don't update until you run generation without this tool open.

The best way to work with this view is to enable Auto Update on the toolbar. The icon on the most right.

Then you can update the preview by making changes in the material and pressing Apply or saving the material.

Remember to turn off Auto Update if you're working on a large world and change the tool from Material Debug Tool.

Depending on your machine this can get quite heavy

It's best to view the preview in Unlit viewport mode so lighting and camera exposure don't impact the colors.