The AH-1W has had about three camo schemes you could model. First, the three-tone gray, green, and black that was worn until shortly after Desert Storm (and is depicted in the MRC instructions); second, the tan/sand colored scheme that saw limited use in Desert Storm; and finally, the modern two-tone gray.
For your camo scheme and decal question, you can kill two birds with one stone by acquiring the "Whiskeys in the Mix" decal sheet from Twobobs. All of the decals are top-notch, with full sets for two-tone gray, as well as desert paint scheme helos. A few of the gray birds also come with some wicked nose art. The instruction sheet for these decals also has painting instructions and colors for the desert and gray schemes. Highly recommended.
Finally, some of these paint schemes will depend on what era of modifications you want your Cobra to carry. Out of the box, the MRC kit represents a pre-NTS version (i.e. the shape of the nose, comm antennas and FM homing antennas). You should check out Cobracompany.com. They make a great NTS update kit which includes all the goodies for a modern Cobra with NTS installed. Whole new cockpit, nose, and plume detectors are offered (plus lots more). The update set is highly recommended. But any way you slice it, the MRC kit builds up very nicely. Let us know if you have any other questions about the kit.
PS, I beleive there will be a new set of AH-1W decals coming out soon....depicting a west-coast Commanding Officer "high-vis" scheme.