The color space of custom map rendering seems to be cut off at some point. Some RGB colors are not being rendered onto the map. If you run the attached plugin on a Spigot server and run

/test

you are given 6 maps on which multiple color spaces are rendered. On several of these maps the color is not at all rendered, showing the blank texture of an unexplored map. The following screenshots also show the 6 maps:

Note that in previous version this was possible and working (for example in 1.15.2) with the same code.