Hi there I need to know what placeholder to use to only show luckperms group color for Featherboard reasons

or is there a way for me to create a custom placeholder like what I've done here with BTLP

You could set the colour code as meta values, then use the meta placeholder.

https://luckperms.net/wiki/Meta-Commands#lp-usergroup-usergroup-meta-set-key-value-context
https://luckperms.net/wiki/Prefixes,-Suffixes-&-Meta
https://luckperms.net/wiki/Placeholders#luckperms_meta_meta-key