I agree with Piaffe really, but you can breed Oldenburg with several types of warmbloods and still get it registered in the Oldenburg registry. Some you could breed with are Norwegian Warmblood, Danish Warmblood, English Thouroughbred. I know for sure that you can register English TB x Oldenburg as an Oldenburg since many of today's Oldenburgs have a long line of TB's in their pedigree to make them lighter and better sport horses. Pure bred Oldenburgs are often very stocky built. If you breed your stallion with a Norwegian Warmblood for eks. Then you could get it registered as a Norwegian Warmblood, think the same would go for a Dutch Warmblood (KWPN). That might be exciting if you were to find a painted KWPN, that has a nice build and pedigree. Don't know what registery you could register an Oldenburg x Arab mix. Not in Europe at least, but I think we Europeans are much more picky when it comes to breeding..which I believe is a good thing. There are so many strange mixes around. Here in Norway it is illegal to crossbreed, unless it's an approved breed. The Barockpinto is on it's way in but I just don't see the point in it. A flashy spotted horse that costs way too much in my opinion :P So much cross breeding is going to make the original bloodlines die out eventually. If I could keep my mare I would definetly breed her, I love her pedigree.
Breed for quality, I wouldnt think too much about the colour.
Sorry if I got a bit carried away, I love studying pedigrees and i'm in a couple of breeding comitees so I find it all very exciting :)