Sorry for the late answer. I have no exact figure of how many Colours and Standards belonging to the old Imperial Army that was taken by the Allies in 1945. But the Book Flags of the Third Reich 1: Wehrmacht by Brian L. Davis and Malcolm McGregor mentions that in 1914 the Imperial Army possessed 877 Regimental Colours, 105 Standards, 337 Landwehr Colours and 21 Landwehr Standards. Of these the following where lost during or after WW 1 51 regimental Colours, three Standards, 25 Landwher Colours and two Landwehr Standards. Apart from this 65 Colours and Standards where deliberatly burnt at Posen (Poznan) on 21 November 1918 to prevent them from falling into Polish Hands. So this leaves several hundred Colours and Standards of the Old Army to be taken by Allied Forces, but as said I have no information of exactly how many of them who suffered this fate.
It should also be noted that during the Time of the Weimar Republic no new Colours or Standards where presented to the Units of the Reichswehr. They continued to use the old ones until new ones where presented begining in 1936 to Units of the Wehrmacht.