NiiVue comes with many built-in colormaps, which you can explore in this live demo. The NiiVue format is described here.
However, FreeSurfer uses a different format for its Color Lookup Tables. This Python script converts files in the FreeSurfer format to NiiVue's format. The script will convert all the text files (*.txt) in the folder to JSON files. The included color tables are from PyROI
git clone https://github.com/niivue/fs2NiiVueColormaps
cd fs2NiiVueColormaps
python fs2niivue.py