Yep, what they said :)
You might try
http://www.mohawk-finishing.com/catalog_browse.asp?ictNbr=120
If you can find the color match. The photo doesn't look that white, but, Ultra® Mark White Melamine #1 #013481 Is one I would look at.

For a one time thing, it is probably easier to match the color at the paint store. They may even have the color on record if you give them the brand name and color of the cabinets.
Sheen and texture are very important to getting a good match. Try this on a test board and then have another 'control sample' painted at the exact same time you touch up the cabinet;
Get the slightly shinier paint rather than too dull. Then put some on a test piece of a similar material. When it is almost dry, wipe it with denatured alcohol. This will dull the sheen slightly and give it a more compatible texture. This takes good timing, so try it first, noting the time it takes as you try it on different parts of a test piece at different times from a little too early while it dries in your kitchen. Then do a test piece when you actually paint the cabinet to avoid the temptation of touching the cabinet to see if it is dry enough, and wipe the test piece with alcohol before the cabinet to make sure it is the right time.
For this touch-up, I think I would do as small of an area as possible. Since it is behind the door, keep it behind the door.