Coloring is a general purpose weapon.  It limits the puzzle’s  ability to satisfy the restrictions imposed by  Sue de Coq and APE .  This explains why sysudokies  record the “almost” patterns found in the bv scan, and return to them when an extensive cluster does not collapse the puzzle.

An example is the Delta Sky “Even More of a Challenge”  of June 2008. After box marking:

1: NWm=>Wm. 2: Nm, Ct=>N2, SW2=>Wm, Em.  3: C3=>Nm, NWm, SE3=>NEt.  4: Cm.

5: Sm, NEm.  6: NEm, Wm.  7: E7=>(NEt, E5m=>W5t), Sm. 

8: N8=>(Cm=>Sm, N7m), SWm=>W8=>(C8, W2).  9: NEr2np69, SEm=>S9=>Ct, Wm.

and line marking:

3f: r4, r9, c3  4f:  r3, c5, c6., c7, c8  5f: r1, r5, r6, r7, c2, c4, c9  6f: c1  Closure r2, r8.

there is a 345-wing hinged in NW removing three candidates,  and  SdC in Er6 removing three.   Then your blue/green cluster encouraged by available slinks and bv  yields two decisive 7-traps, as seen below:

More to the point, however,  is the effects of coloring in chute Nr2. 

Sue de Coq Nr2=5(1+7)(3+4) is trimmed to 531 if blue is true, and 547 if green. Also  the APE r2c56 that without coloring, allows  14+31+37+41+47, is now limited to 31+47. Two candidates are removed by either technique, creating two more bv and extending the cluster.

My early nemesis became a case in point that previously unsuccessful SdC’s and APE’s might well be enabled by coloring effects.  I’m grateful that I could save in detail my earlier struggles with the Delta Sky “Even More of a Challenge”  of June 2008 in a © PowerPoint presentation file.  Take this to heart and request a grid template and bv and xp maps at sysudoku@gmail.com .  

This post concludes my series on sysudoku coloring. Next we consider the extension of alternating slink/wink chains by means other than X-chains and XY chains.  It’s where we go in the SSOB with difficult puzzles that avoid effective coloring, or survive it. My first example  exhibits stubbornness of the first kind, and perhaps you would like to  do the basic solving and look for bv scan and X-panel results. It’s Maestro 47 from Megastar, Fall 2009.