Regarding the underside blue, colour is often an argued subject on WW1 aircraft. Curiously I too did the underside of a DR.1 in grey, it was so long ago that I cannot remember where I got the reference from - it may have been from the kit manufacturer. A light blue/green is also depicted but the only fact I can say about colours is that we do not know for sure what they are and may have even varied form DR.1 to DR.1. On reading a description of how colour back then was mixed the writer stated that X number of handfuls - yes handfuls of different pigments were mixed into varnish. The varnish also had a yellow tint to it. This does give one great advantage - artistic license. In my opinion you cannot really be wrong as far as aircraft colours are concerned.
Alan.
