Colonial powers no longer interested in expanding their colonies?
Hmm, I think that not all top powers would be in the same boat in this issue. Some would be happy with what they have, true: the British and the USA. But others, including the French, and then especially the newcomers (Germany, Italy, Japan, others) clearly showed, in the years just before WWI, that they still wanted larger slices. Think of the Agadir crisis: the French were not through with Morocco, and Germany and Spain wanted compensations. Think of the Italian war on Turkey that gave Italy Libya and the Dodecanesus. Think that Japan completed its annexation of Korea just in 1910.
So yes, those bits that are still out there would in all likelihood still need to fall under control of a colonial power. Others have already mentioned it, Ethiopia, Mongolia, Siam, and for the really hungry, the Ottoman Empire. Maybe the British and the USA would pass, this time; or maybe they'd decide they need to contain the competition by competing themselves. It's possible that they'd go for informal influence rather than direct colonial annexation, but they should beware; the French and the British thought they were vying for that in Addis Ababa, and that it would suffice, but brute force was shown to be able to trump that.