It looks like a clever way to visualize the problem, and to make the ‘guessing’ easier. Instead of putting for example tiny eights and nines, you simply decide you’re testing nines and run true/false checks to see if it’s possible. Easier than going back and erasing.
In twickster’s puzzle there’s a couple of squares where it can be either a nine or one other number. These have corresponding squares in the same group (row, column or 3x3 square).
Row 1:column 6 is either 8 or 9. A conjugate pair is found at row 3:column 4, also 8 or 9 and mutually exclusive. Looking only at the nines, we find that this has a conjugate pair in R4:C4 - either a 3 (doesn’t matter, only looking at the nines) or a 9. This leads to R4:C3 and R6:C5.
And you keep going, alternating between blue and green until you find an impossible situation with either colour (two of the same colour in the same group). The other colour then is where you want to put your 9s.
Hmm, not as clear as I was hoping. Sorry, it’s early.