The white ones are called milkies, they and the experiments both originate from orsoniks previous games, not sure how far back milkies go but they were from gunsaw to my knowledge. There are plenty of other species in gunsaw that could potentially be brought over to casualties unknown, though I am unsure on the timeframe of all this, cause gunsaw is a decent chunk in the future compared to casualties unknown, plus experiments are described to be the first species brought in large numbers to the planet on which both games take place. Maybe a couple more species could be possible cantitades for addition into casualties unknown, idunno really.
On milkies themselves though, they are described as dextrous but frail specimens, with incredible intelligence and they tend to speak in a formal manner, though I havent actually managed to notice the difference between milkie and experiment communication.
Experiments have also been described as being basic, a template for all the other species, there isnt much special about experiments.