Bird feathers are somewhat rare in the fossil record but some circumstances allow them to be more easily preserved. Such is the case in the Parachute Creek member of the Green River formation. The Parachute Creek member is an oil shale that was deposited by a series of freshwater lakes in the Eocene located in northwestern Colorado and northeastern Utah. Here are some examples of the feathers that can be found within these fossil lake deposits.
All three of the feathers look to be fairly simple and could just be down feathers. Sometimes color patterns can be preserved but I don't see any on these.