The milky stuff looks kind of like oil-water emulsion (oil blowby mixed with condensation from the incoming charge air that’s being cooled in the intercooler. Especially if you live somewhere humid.
The yellow color is a bit odd though - the only two things that come to mind are either dye in your oil, or a really weird possibility is if you’re using an aftermarket air filter, and also live or drive near one of those awful street trees that splooge yellow pollen everywhere (which tends towards the smaller particle size and a fraction of it will get through the filter). Pine, cedar, pepper tree,etc. There’s one of the latter in my neighborhood and the person that lives there parks a car under it that’s constantly covered in nasty fine bright yellow dust. If you live or work near trees like that, you might find some of the yellow crap in either your engine filter or cabin air filter, though road dust might cover up the color. If it actually is pollen, it’s not harmful to the engine like typical silica and dirt, other than clogging up the air filter.
Barring those two possibilities it could be anything with yellow dye that goes in the car, or possibly something that reacts with moisture and blowby and drops out with the condensate post-intercooler.