The Vital Strike feat (standard action to use) doesn't work in conjunction with the Spring Attack feat (full-round action to use). (I would assume that the same applies to the Fly-By Attack feat, despite the wording of that feat.)
So the COoS can either a), move a bit, attack normally, and move some more (total move no more than 50'), or b), single move (max. 50') into its range (15', which is far longer than most PCs with weapons), then Vital Strike. Unless it gets hit by a lot of de-buffs, it will automatically make its Fly skill check to hover.
I'm no expert in de-buffs, unfortunately. It also depends upon what your players' party has available (which classes/levels and magic items, and how much of their resources they've used up when they encounter the COoS).
If you are really worried, then add a useful piece of treasure to an area just before they get to the COoS. Maybe a Wand of Magic Missiles with 5 to 10 charges left, possibly maximised and at caster level 9? That would inflict 25 points of force damage per charge (assuming that each individual charge from the wand penetrates the COoS's Spell Resistance 21).
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It's been discussed a whole lot in the rules forum. The basic conclusion is that, because of the wording, Vital Strike does work with Flyby Attack, but it does not work with Spring Attack.
So in the Colour's case, it can't Spring Attack/Vital Strike.
That doesn't mean it won't still brutalize your players, of course. It's extremely hard to hurt unless you've got a force caster. Maybe you should add a bead of force or two into the loot somewhere. They could chuck it at the Colour, and then just run away.
I'll tell you how my party faced it: the Color chewed on the face of the beefy fighter repeatedly until he was almost dead, and the rest of them tried to keep him alive while a couple of others figured out the Force vulnerability and used that against it. They practically had to almost sacrifice a PC.
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I ran the Color Out Of Space in a homebrew mashup of (From Shore To Sea, plus my own stuff, plus some additional AP material.
I used the CooS as the end-boss.
I had the creature chained to an adjoining room via a magical force cord. This limited its movement to some extent.
I also place restriction on the cavern ceiling to about 30' which limited movement a bit more.
It is no doubt a SERIOUS threat to your party. Thus I further restricted its "incorporeal" status to being able to be hit normally and story-edited the silver force cord as having been placed their successfully by a previous adventuring party who suffered a TPK. The cord was designed to "tether" the beast to the material plane, thus removing its "incorporeal" monster traits.
With all those restrictions in place, I put it up against my (then) Level 6 adventuring party. They are seasoned gamers (think every good choice possible in combat is usually made; probably 150 years of gaming experience at the table) thus I treat the player group as CR+2 for normal encounters (APL+2, and shift the hard challenging and epic encounters accordingly).
Perhaps this helps you a bit. I don't know what level your party is, but if they're already at least CR8 and possess a few ghosttouch weapons or force missiles you should be fine without these restrictions, but if not, may you can use some of these ideas.
Hope that helps,
P.s. The players LOVED the creature. Awesome ending for a great story.