Dry Pasta Salad

Is it inevitable that a mayonaise-based pasta salad will absorb all the mayonaise and turn kinda grey in storage? I hate to mix more mayonaise in all the time, largely for aesthetic purposes. I mean, I think pasta salad is bad enough for me, anyway. I don't recall my mom or grandmother having this problem, nor can I imagine that deli counters across the country add fresh mayo (or whatever) to their pasta salad selections every morning. Is there a trick of some sort? A related problem I have is trying to store left-over homemade soup -- giant noodles, rice mush, barely sludge and the like invariably insue. Campbell's and the like don't have this problem, though perhaps their methods can not (or should not) be adapted to the home kitchen.

Thanks,
P