Top layer shading
The top layers of my prints, noticeable mostly with black petg, is lighter near the top right hand corner of my top surfaces. I have tried extrusion calibration, speed, # of top layers, cooling adjustments, etc. I am using a Prusa MK4. Any idea how I can get the top layer more uniform and what is causing these odd outlines?
RE: Top layer shading
If you run your fingernail perpendicular to the lines, can you feel that they are each a tiny ridge? If so, that looks like over extrusion. You've already adjusted the extrusion multiplier but maybe try even lower numbers. It would likely affect the rest of your print as well but it would at least give you something to go on.
Another thing to look for could be filament clinging to the nozzle since PETG is notoriously sticky. It may be that by the time the print gets this far there is a buildup of PETG on the nozzle that is just dragging back and forth, dragging a blob through the just-deposited filament.
RE: Top layer shading
The very first thing to check is the bottom under that corner and edge for ANY slight lifting. If there is any then the shading will be different just like the top. You often get top surface artefacts like that when the layers are slightly more compressed due to a slight lift.
If it was straight forward over extrusion then you would expect to see that over all the top, not just in specific areas.
If theres zero lifting on the bottom then I would reslice and change the top surface angle to see if the artefact changes position.