I suppose TakaraTOMY were going with Rodimus Prime as he first appeared in the movie, where he still had Hot Rod's magenta; it wasn't until season 3 aired that Rodimus was maroon. Also, since a major selling point of MP9 was changing from Hot Rod to Rodimus Prime, it would be more 'acceptable' to have a magenta Rodimus Prime than a maroon Hot Rod, although the Rodimus Prime Winnebago on MP9 had maroon at the front.
For Hound, TakaraTOMY could have the desert sand Detritus repaint.