They are called mink. All mink-based rats have that pattern, it's most obvious at about six to eight weeks and eventually disappears. Mink is on the site, but they don't talk about the 'moult cap'. Sometimes the moult patterns can be pretty cool, with stripes along the body. Mink hets have the moult cap too, but only weakly. If yours have caps which are almost white they are probably rr or pp.
I don't think we have any 'true hairless' rats in Australia, but double rex rats can be hairless for a while during the juvenile moulting stage.
We have all combinations of mink, ruby-eyed and pink-eyed dilutions in black (aa) and agouti (A*). We also have black-eyed whites (including head-spotted and blazed hets, and some nn patch rats/mm BEWs), albinoes and nn pp C* pink-eyed whites. Mostly hoodeds but lots of Berkshires and selfs too. We have a small number of rexes but deliberately avoid making double rexes. The only colour we don't have is blue, and there are at least two pattern types we don't have (downunder and variegated).
Patch rat
Black-eared black-eyed white
"Mink cap"
A moult cap with a funky triangle on the back
Head spot/patch
Blaze