I know the mechanics of the spell. Pathfinder has a habit of tripping me up on things that I misremember from other systems. I'm looking to check that I haven't missed any of the small details.
Color Spray's three effects are:
a) Unconscious - I believe nothing they have protects against this effect.
b) Blinded - Tremorsense could be used to negate the reflex save or fall over, assuming that they are i) on the ground, ii) able to use that ability and iii) Most importantly, your DM agrees (YMMV).
Using RAW they still have to make a acrobatics check or fall over when they move more than half speed. Once in range of their target however tremorsense (if valid) lets them hit the target with a 50% miss chance due to being able to pinpoint the square. They still suffer all other effects of being blinded
c) Stunned - Elementals are immune
A Small Earth Elemental is a 2HD creature, so it would normally get "The creature is unconscious, blinded, and stunned for 2d4 rounds, then blinded and stunned for 1d4 rounds, and then stunned for 1 round." but elementals are immune to the stunned effect so that would leave you with "The creature is unconscious and blinded for 2d4 rounds, then blinded for 1d4 rounds."