In a 1918 victory, regardless of Germany's position in France and Belgium, I don't think they'll get much of anything. I mean - Togo and East Africa are occupied by Britain; Southwest Africa is occupied by South Africa; Kamerun is occupied by both Britain and France. I think Belgium, even, occupied parts of East Africa (Rwanda-Urundi of course, but I think they were further into the centre as well).
So what if Germany has control over the Belgian and French governments? They can, what, get them to issue the order to release Kamerun and part of East Africa. Britain then moves in and takes the rest. They've got German oceanic trade and the colonies as hostages, and remember in Versailles South Africa was considered its own party (meaning Britain couldn't very well just tell them to give back Southwest Africa).
You might see the return of some colonies in exchange for the independence of France and Belgium. I think Germany having a free hand in the east is a given, considering the collapse of Russia, but what's the most they can hope for? Britain still wants their (theoretical) Cape-Cairo link, so East Africa will remain in British hands. South Africa always saw Southwest Africa as a natural part of their country and their own little colony, so I don't see them giving it up. Togoland was the only profitable German colony, and it was small, so maybe that's what they get back in Africa.
I don't see Britain giving them everything, and I don't see them allowing the Germans to annex swathes of French Africa either.
The powers of WWI were more evenly matched than people like to admit, I think. At a stretch, I'd say a return to the status quo ante bellum could happen, meaning German Africa will return to its pre-war state, but so would the rest of Europe (excepting of course the east). Independent Belgium would return, independent France as well, and the Germans would have proven themselves a force to be reckoned with but obviously unable to defeat the RN.