Avenger can't memorize Chromatic Orb upon character creation

KingGhidorah

When creating an Avenger, Chromatic orb is not available at the section where you can pre memorize your spells.
It might be similair for the higher lvl Avenger spells should you create him at a higher level.

You can memorize it without problems once you've completed character creation and start the game tho.

Avenger_teambg

It is handled separately as kit ability.
It is indeed not possible to assign as memorizable in chargen (bg2 was similar).
Implementing this would be just too difficult.