(Quoted from Nazdar Ink Technologies. Full article here.)
G7 is the colour control methodology that achieves colour similarity across all print processes. The method balances the four primary process printing colours, CMYK and their three overprints RGB (the 7 in G7) to achieve neutral grey (the G in G7) in a raster image. This methodology was created in 2006 by Don Hutcheson and used primarily by the offset lithography printing process at that time.
In 2008, Nazdar Consulting Services introduced the G7 methodology to the screen and wide format graphic ink jet printing processes as the best way to achieve a common appearance in images when printed on different substrates, using different printing processes. This was a big departure from the existing printing specifications (SNAP, GRACoL, and SWOP) which were specific to the offset printing process on a certain grade of paper.
Click here to read the full article