This has me puzzled. It shouldn't be transmission fluid, What about hydraulic brakes? Is there any leakage from your hubs? Be sure to look at the inside of your rims also. That is usually a brown fluid, but dang, I just don't know what is going on. Are you sure it's coming from your tractor and not another vehicle? I've got an old truck that I plow with, and when I plowed fresh snow, I would find pink spots. I went through that truck over and over, never finding anything. I realized one day that the bulk of it was where my wife stopped backing from the garage to go foreward out the gate. Popped her hood and the tranny cooler line in front of the radiator was leaking. Only saw it after plowing, and it only leaked when shifting from reverse to drive. Good luck!!