OK, I'm kidding (a little). Colleges don't have a special affinity for stamp-collectors any
more than they do any other activity. What colleges love is passion. It
really doesn't matter what your passion is–dance, art, sports,
reading, rodeo, student government, working a part time job at a burger
joint, juggling, magic or, yes, stamp collecting. A kid becomes much
more interesting to an
admissions officer when that student is genuinely passionate about her activities.
Colleges would, in fact, appreciate a student who was super-serious about stamps. The more into it you were, the better. They'd like the kid who visits stamp shows on the weekends, who reads stamp-collector magazines, who belongs to stamp-collecting organizations, who takes classes and writes articles for stamp-collector newsletters.
So go after your passions. Celebrate them. Take them to a reasonable and productive extreme. And don't worry whether the colleges will like them. If it's important to you, and you inject your intellect, talent and energy into it to make something happen for yourself or others, the colleges will care about it, too (as long as it isn't illegal).
And when you apply to college, share your passions–in the applications, in the essays, and during your interviews. Help the colleges learn about them. Don't keep them secret.