I've never been able to see spells an Evoker can purge while they have the Scouring Flame PvP talent selected. I am unsure if this is since Evokers can't purge baseline, if this is impacted by a non-KNP setting, or something else is causing the issue.

The purgeable highlighting works for every other class that is able (Mage, Hunter, Priest, etc.).

Related: A setting I would like to see implemented, or perhaps is already and I am missing it, is to highlight purgeable spells for all non-purge classes.