The option to edit a custom colour palette in "Options -> Color" has been removed. This wiki tells me to look under Format Area or Format -> Area: https://help.libreoffice.org/Draw/Defining_Custom_Colors But neither exist. Se created question by CupcakeMedia: https://ask.libreoffice.org/en/question/129227/how-to-editcreate-colour-palettes/
Thanks for reporting the issue! That help page is indeed out of date. See bug 107079. *** This bug has been marked as a duplicate of bug 107079 ***