I agree. Sleep is better in the perfect circumstances, but color spray is much more robust.
These are the spells that immediately come to mind when a spell level is mentioned. That doesn't mean that all arcanists will have all of them, obviously, but almost all arcanists can be expected to have at least one for each level, unless they're making some sort of point:
0--detect magic, prestidigitation, mage hand
1st--magic missile, mage armor
2nd--scorching ray
3rd--fly, fireball, haste
4th--dimension door, improved invisibility, polymorph
5th--teleport, overland flight
6th--distintegrate, superior resistance (if SC is in use)
7th--limited wish
8th--...?
9th--...? I dunno, haven't seen many arcanists at those levels