(I don't think anyone's posted specifically this yet.)
Now that NQ has confirmed that Colossals are Warjacks, and we already knew they were part of the Battlegroup, here is a list of Caster interactions as such:
Infernal Machine, Feat (to give Pseudo-Stealth)
Seas of Fate
Shadowmancer (only Dark Shroud)
Add stuff if I missed it.
Also, the Warwitch Siren should work as well as the ILO, but the Colossals can't recieve Stealth.