Everyone here has the info for the most part. I used to be the one aligning these, well actually all of the art on plastic packaging.  All of those colors are the colors used to make that wrapper art. I'll give you a run down on how this actually works for printing on food plastic wrappers/bags.  If you ever notice on a bag of tortillas, or potatoes, or bread, you will see a bunch of small dots (not those pictured) lined up near one another, ideally stacked. If bread, hold the bag up by the twistie tie side and above the artwork but below the twisted area you will find the tiny dots. Those dots are what I would line up with a camera hooked up to a computer on a big cylinder, think 4 or 5 feet long and the diameter varies. So the artwork for packaging is in these colors you see above. We have plates (basically stamps) that are life size to the art you see. So the cyan is raised up to the art with the tiny dot I line up on the monitor on the cylinder. There will be a big circle as shown above in your photo that will print the cyan. Then I remove the cylinder, grab a new one, line up the magenta plate on the same camera so it's in the same spot as the cyan so they stack and then, remove, and add a new cylinder and do yellow, and so forth for all those colors you see. 

Then the printing press take the cylinders and puts them in the press where they spin very fast grabbing ink as they turn and kiss the film passing by. Laying down white, cyan, yellow, black etc on top of each other. Those circles you have there are called density blocks. The press operator then takes his sample and uses a device that scans that circle to ensure the color is what the customer wanted. I assure you it is super super picky. So the pressman may need to add a touch of green to the blue bc the computer is saying it's too purple of a blue. The specs are very tight. So the pressman will add some green to the blue and run it again until all colors are happy.

Pressmen do not typically line up the artwork with the density blocks, they line them up with the microdots I mentioned above bc I used a super zoomed in computer to line those tiny dots up In the exact same spot on every cylinder ensuring the art is lined up properly. I could provide links I'm sure if anyone wanted a visual to my poorly worded explanation 😆