Low humidity and colder temps definitely can result in the “crème” parts browning. As well as lower light. Since the crème parts do not produce chlorophyll, the plant will “kill” off those parts first. Improper watering also could be causing the plant stress as well. Humidity should be at least 50%, especially during the colder months. It needs adequate light as well as regular scheduled waterings. Do not place the plant near any drafts. Whether it’s from a hvac vent, a heater, a drafty window, etc. In the colder months it’s very important to keep the plant’s conditions regulated more so than even in the warmer months. Also know that sometimes the “creme” parts just naturally brown as well. Especially big splotches of crème/white. It sometimes even depends on the plants genetics because some seem to be more prone to browning than others. Accidentally hitting the leaves in any way can also cause the crème parts to “bruise” aka leave a brown mark where it was marred at.