An example of a forcing chain present in this puzzle and not included in the "coloring" category is:
[r7c7]-7-[Almost Locked Set: r8c9|r9c8|r9c9]-4-[r2c9]-7-[r5c9]-1-[r5c7]-7-[r7c7],
which means that, if r7c7 is "7" then r5c7 turns out to be also "7". So, r7c7 cannot be "7" and that solve the puzzle.
Carcul
