This is a nice photo. The hay is nice and golden, but, as you said, the background is a bit grayish (?). You could select just the color cast area and manipulate the curves and levels then. That would be my suggestion. Or try burning/dodging, darken the area. Are you using your camera's meter to expose? That could be part of the problem. Try taking separate meter readings of the background and foreground and then average the two. That would probably give you better light. Just a suggestion. A nice comp and keep up the good work.

Dzerzhinski