Some helpful info with InterfaceOptionsFrame_OpenToCategory

[Nightness]

This is used to display a specific addon's settings in Menu -> Interface -> Addons...

Call this function twice (in a row)... There is a bug in Blizzard's code which makes the first call (after login or /reload) fail. It opens interface options but not on the addon's interface options; instead it opens the default interface options. If you call it twice in a row, it works as intended.