First and foremost, consider the nature of the works you cite. When 1st edition Advanced D&D (aka 1e) was written, roleplaying was still new and error-correction and (extensive) rules extrapolations had not yet occurred. Worse yet, this rules set was written while Original D&D was being played by everyone, including the 1e author Gary Gygax. Several errors (see footnote) occurred during this overlap phase, and a general lack of specificity is common, most rules being left to the DM's logic and discretion.
Any question demanding a "by-the-book" (BtB) 1e ruling is thus subject to these errors and omissions, and the answer may be contradictory and/or illogical.
The first-level illusionist spell color spray operates by overloading the senses/neural networks of its subject.
Sorry Rich, but 'overloading the senses' is your deduction, and is not BtB. We can only say (BtB) that the 1st level spell (i.e. minimum power) causes unconsciousness, blindness, or stun, and that some victims get no saving throw.
Our view is that the same lack of conventional consciousness that makes the undead immune to sleep and charm also makes them immune to color spray.
While this is a logical sentiment it again is not supported by the Rules As Written. Nowhere do the rules refer to a 'lack of conventional consciousness'. Although it is a logical deduction, your BtB emphasis again precludes it.
It is true that most undead are immune to sleep and charm effects. But note that a Ghost is not explicitly given those immunities. This was probably a mere omission -- but again we have the BtB issue. (Deductions about immunities of undead as a class may also be faulty; many undead are also immune to hold and cold effects, but the Ghost is not, nor are ghouls or ghasts.)
THUS: given the descriptions in Monster Manual (1977) and lacking any explicit prohibition in the subsequent volumes, the Players Handbook (1978) and Dungeon Master's Guide (1979), the BtB ruling should be that Color Spray affects all undead mentioned in those works (Skeleton, Ghoul, Shadow, Wight, Ghast, Wraith, Mummy, Spectre, Vampire, Ghost, Lich).
In my own games I apply additional deductions and agree with your stance. But strictly BtB I must respectfully disagree with the other answers offered here.
Corollary: Don't insist on BtB answers for 1e. ;)
- One of the most famous contradictions of the OD&D/AD&D crossover period represented in the 1e rulebooks is one At-Will ability of the Demon Yeenoghu, a "magic missile... having a +2 to hit" (MM1 p20, 1977) although the magic missiles (per spell) "unerringly strike their target" (PH p67, 1978).