That would be either the transfer unit or the fuser.
Just pull them out and take a look, probably you will see the problem (dirty damaged rollers, belt)
It could also be contamination if it sat for a long period, or even more if it was moved/tilted. Which would likely be fixable by running 10 solid full color sheets, then 10 blanks (First 10 clear any clogged particles, 2nd 10 clean any spilled waste)
Unless of course there is in fact damage, in which case replacement of the part is necessary.
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