This most likely means he has been cleared by doctors to resume full contact. It could also mean he plays in the game today although I have my doubts.
Dennis Allen had said Hayden was expected to be cleared by doctors today, but he also added he would probably not play until week three when the Raiders host the Chicago Bears at home.
Hayden was the team's top pick in the 2013 draft (12 overall). He has been wearing a red non-contact jersey all of camp after a surgery to remove scar tissue from his abdomen back in May. This is at very least the first time he has been seen out of a red jersey since the team's first OTA practice, prior to the surgery.