Work ethic is always black, and it moves fastest around the middle. As a four year starter, he'll gain 25-30 points of work ethic over his career (it moves up noticeably slower under 20, but at 25, you should get 6-7 per year, as long as he starts all year). You should be able to max his cores. A non-core or two may have to wait until his junior/senior year, and then may not max, but should be able to get well into the black.