Quote Originally Posted by Grim Reader View Post
At the bolded: Whut? As far as I remember the relevant RS text is the standard text, not the Eldrich Knight.
Quote Originally Posted by Complete Divine
Spells per Day/Spells Known: When a new rainbow servant level is gained, the character gains new spells per day as if she had also gained a level in whatever spellcasting class in which she could cast 3rd-level arcane spells before she added the prestige class.
Underlining mine, but it is clear - if you enter Rainbow Servant as a Wizard 5 / Duskblade 1 / Beguiler 1 / Warmage 1 then RS can never be used to increase the casting of any class other than wizard.