If Germany is going to be allowed to keep their colonies for... some reason, it might mean a peace we can't recognize, but if we try to hammer it into the framework of what existed at Versailles as we knew it:
- Germany might only nominally 'keep' the colonies, and administer them as mandates under some other power's observation under the League of Nations. This might keep them under the German flag but would remove them from any kind of serious consideration, especially given all the restrictions that were places on mandates and how they could be developed.
- If Germany does keep her colonies, she has good reason to plead for more allowances in terms of an army and a navy, to defend and police these far-flung corners of the world, over and above the force limits imposed at Versailles.
- Keeping the colonies may come at the cost of some other concessions on the part of Germany, but what I can't imagine.