Mantled Eridite rainbow servant

[Renen]

With magic mantle Erudite can technically cast arcane spells, since psionics and arcane are the same to them. Would I qualify to enter and receive full bonuses of rainbow servant? (Seeing as you add its level to "whatever class that allowed you to cast arcane spells")

[Maginomicon]

You have a false assumption. That's not actually what the magic mantle does:
You gain Use Magic Device as a class skill. If you purchased ranks in Use Magic Device or Use Psionic Device at the cross-class rate, you get additional ranks in Use Magic Device or Use Psionic Device as if it had always been a class skill for you.

In addition, you always treat magic and psionics as identical. Therefore, powers such as dispel psionics work for both magic and psionics. Most campaigns already treat them in this manner, so this mantle is most useful in campaigns where they are considered different systems.

(Emphasis mine.)

The bolded section is referring to the optional "Psionics is Different" variant (Expanded Psionics Handbook page 65), which has psionics not interfere with magic and vice versa.

[Renen]

Aww... pity.