This could have been part of the run of 50 'Wendell - Long Mane/Tail Version'. Unknown if this was part of that run or a separate run of one or more. Painted in a Palomino Tobiano pattern with striped hooves, four socks and a blaze.
The model 'Big Rex aka ISH Thirteen' is a OOAK version of that same paint job: http://www.stonehorseref.com/node/14898.