When expressing chroma subsampling ratios the 4:2:2 doesn't refer to primary colours as G:R:B, it's Y:Cb:Cr which refers to Luminance (Y) and two colour difference components Blue Difference (Cb) and Red difference (Cr)
I think that they are one in the same (G:R:B and Y:Cb:Cr) in this application, but I'm not certain.
The 4:2:2 is a type of chroma sub-sampling.
Since the human eye is more responsive to brightness than to colour it is possible to save space when storing an image by storing more brightness values than colour values. This is done by converting the RGB colour space to Y:Cr:Cb. The colours (Cr,Cb) are then sampled less than the brightness (Y) when the image is saved.
Note that the Y:Cr:Cb colour space can be converted back to RGB (it is simply a different 3-dimensional representation of the same data). Missing Cr:Cb values are filled in from surrounding values and then each pixel is converted back. This is done when viewing the movie.
Check out the Wikipedia article that has a few picture showing how the image stored in different sub-sampling schemes looks:http://en.wikipedia.org/wiki/Chroma_subsampling
The subsampling scheme is commonly expressed as a three part ratio J:a:b
J: horizontal sampling reference (width of the conceptual region). Usually, 4.
a: number of chrominance samples (Cr, Cb) in the first row of J pixels.
b: number of (additional) chrominance samples (Cr, Cb) in the second row of J pixels.
From this you can appreciate the 4:2:0 is worse than 4:2:2 since the former will only change colour every other horizontal line. Both will change colour every other vertical line. The holy grail is 4:4:4 since that does not throw any information away. If also takes up more space.
The second factor in quality is how many bits are used to store the data. Canon DSLRs use 8-bits (values from 0-255). The Cinema cameras use 10-bit (0-1023) or 12-bits (0-4095) so get a lot more gradation of tone. This also takes more space.
I believe the combination of sub-sampling, bit-depth, image size (e.g. 1920x1080) and frame rate (e.g. 24/s) are all combined to create a bit-rate for the movie. This is how many numbers are passed through the system per second. It is this final number that states the overall quality of the system and also the type of storage media requirements involved.