LB, I agree with the above post. People who wear black velvet kippahs tend to wear them for everything. There are some sects of Yerushalmim that wear a white kippah on Shabbos and YT (and thus for a family simcha) with their streimels. Also Na-Nach Breslovers probably wear more white kippahs. There are also people who wear the knitted kippahs that might be white or any other color of their choice, not necessarily related to the place they are going. People who wear the white silk/polyester kippahs, like the kind CTLawyer is mentioning, with names embossed on them, are not necessarily wearing them except at the simcha itself.
Could you clarify what kind of white kippah you are referring to.