I read years ago that it has to do with the way that light reflects or refracts (sorry, don't remember which) off skin with makeup vs. without. The solution they recommended was to brush powder on your neck so there's no stark difference. And if you are wearing a strapless dress for say a formal event, maybe even down to the chest.
A family member had her prom this year and the MA brushed some powder on her neck at my request, although the liquid foundation had SPF in it and the pictures came out fine.
Might be worth a try!