I was getting it too from my Starry Night Cutlass. I figured it was either freboard oil or gunstock oil residue, stain or a reaction from the steel strings or frets. I believe it came with steel hybrid slinkies. When I did my first string change, I gave the fretboard a good rubdown with EB fretboard conditioner and put regular slinkies on it and it has GREATLY reduced the dirty fingers. It's like 10-20% of what it was.
2016 PDN Starry Night Cutlass (Natural Headstock)
2010 Barolo JPX (Piezo, Inlays, Matching Headstock)
2007 Bahama Blue Sparkle Back BFR Luke (GC Exclusive)
2007 Blue Dawn LE JP6 (Piezo, Inlays, Matching Headstock)
2006 Dargie Delight Luke I (No Piezo, Natural Headstock)
2005 Sapphire Black JP6 (Piezo, Inlays, Matching Headstock)