Head clog banding will be visible in the color associated with the clogged nozzle. It can be very subtle sometimes, such as in blue skies when you have a single Cyan nozzle clog.
I usually do an indirect nozzle check by printing vertical crops out of the next image to print, mostly as a test swatch for the image but also to check for head clogs. Since my 7800 has minimum print length of 6", I usually gang together 2 or 3, 2" x tall crops out of the image. If the test swatch looks clean under slight magnification, I go ahead with a print. If not, I go down the head cleaning path. For a sheet printer you can just nibble away at a 13x19" sheet...cut off the printed swatch each time. Keep a directory of images-to-print so you always have a candidate image for a swatch. Or you can just do a nozzle check.
For most parts of the country Fall is nozzle-clog season, get used to it! Doesn't take long at all for clog to develop (on some printers) you need to keep ahead of it. Friend of mine keeps his 2400 under a plastic cover with a wet paper towel applied to the flip-up printer cover, swears it works great!
