i used to work for a newspaper company and one of the things we had to know in our orientation was the paper and ink quality.  yeah, i know, weird since i didn't actually work w/quality control.  i worked in customer service and collections.  lol  
anyway, the black n white sections (newsprint) is normally printed w/a soy ink, that's why it usually comes off on your hands.  it's inexpensive and completely nontoxic, as well as washes off w/out staining your hands or clothing permanently unless you work w/it 8-12hrs a day.  then it's a heck of a mess.  the other pages w/colored print like the flyers...those are NOT printed w/soy ink.  those are commercial grade dye and those are NOT nontoxic.  that's why they do NOT come off on your hands.  these cannot be ingested w/out ill effects over time.  
newsprint can be used in cages w/out a grating, but the colored flyers should ONLY be used when you can guarantee that your pets cannot reach them to shred.  the paper quality AND the ink quality is dangerously toxic to them if mouthed, licked, or chewed on over time.  
maria