I know, but Neanderthals weren't one of those three ancestral populations. Those three (proto-)white ancestral populations emerged thousands (if not tens of thousands) of years after the Neanderthals were still around and the mixing occurred. Those three acestral populations were the Western Hunter Gatherers (Nordic whites, Northwestern Europe), Indo-Europeans/Yamnaya (partially Nordic whites, eastern Ukraine and the Caucasus), and Neolithic Farmers (non-Nordic whites; Southern Europe, North Africa and the Levant/Near East). All three of those ancestral populations of mordern-day whites already had Neanderthal admixture, just like non-white Caucasoids, Central Asians (Caucasoid-Mongoloid hybrids) and East Asians (most pure Mongoloids).

Furthermore, West-African blacks (Congoid Negroids) have admixture of up to 20% of previously unknown "ghost DNA", which has recently been revelead to have been a hybrid of Homo Sapiens and Homo Erectus (a now extinct human subspecies which is known for looking like a racist caricature of a black man, which has been found to have been very lazy and low-IQ), meaning modern day blacks are the closest thing still alive to the Homo Erectus.