We are running a full size sheet with pattern screen and about every 4th or 5th sheet the ink colour changes for about 2 sheets and then prints correctly. I wonder if this is build up of ink on the blanket not transfering properly or the ink tack not correct. Also we just replace the ink rollers, so perhaps we should recalibrate the rip as the rollers may be carring more ink now.
a couple of suggestions
sheet distortion.
make sure your in feed brushes on the feeder are down far enough to keep the sheet from flapping around. the feeder set up air/vacuum has alot to do with blended screens to make solids. ink ductor on full coverage should have at least twice as much movement then what usually comes up on your ink profile. you can always close the keys more. but some screen will do that on this press. the form rollers are small and it doesnt recover fast enough with full coverage.
The impression cylinder grippers may need cleaning or adjusting, that may be the issue. Because there are 4 sets of grippers if 1 set is not maybe set correctly this will present the sheet in a different position thus giving a different colour on the sheet, and then it will clean up then do it again.
Colour changing on sheets every 4th or 5th sheet 
Linear Mode
