Yes, you can splice in chromatophores
but how useful would that be? Humans haven't been naked for tens of thousands of years.
In the strictest interpretation of the question, yes, it would be possible with CRISPR-CAS9 to inject the genes for building chromatophores into human DNA. In addition to the coding for chromatophores, a genetisist will need to include all the required development genetic instructions (so the chromatophores form at the skin, not internally where they aren't useful) and any changes to human neurology to accomodate the information processing required to make chromatophores work as camouflage. Remember that cephalopods have huge brain-to-body ratios to handle the additional processing load of making their skin match their surroundings (in additional to the computational load of figuring out what to do with eight arms).
Brains! Brains! Brains!
If no changes to human brain structure are possible, then there will need to be a reduction in some other capability to make way for controlling the chromatophores. Should this compromise be unacceptable, then changes to brain size/structure will be require which brings up questions about fetal cranium size and the corresponding size of the human birth canal (Women's hips are only so wide and can only pass fetal skulls below a certain girth).
[A more recent thought on brains]
We see in octopii that much of their "brains" are in the limbs themselves. Even in humans, certain types of signals just go to the spinal cord then back to the limb. Given these examples, we may be able to keep the current brain architecture but distribute the processing required to make chromatophores work out to the skin.
There's a couple of interesting implications here. Because of the distance between the brain and the skin, the color of the skin may be part of the autonomic nervous systems which the conscious mind has little to no control over. My bet is that there's a ton of social signaling that can be derived from this kind of a system.
In short, adding the genes for chromatophores is a fairly straight forward task with CRISPR. Massaging the rest of human anatomy & physiology, infant development, and neurology into a viable life form is much more challenging.