Its a little hard to make out but i believe the insignia on the epaulette and plain white feather on the hat would seem to mark him out as a brigade general. Normally all American generals wore blue and yellow as you can see Washington does but the dark blue colour scheme with red facings was used by artillerymen with a slightly lighter blue with the red often used by grenadier and fusilier units. Its possible that retaining an attachment to an older unit they commanded and/or were a part of this individual could have been allowed to add the rank insignia onto their old uniform.