@ShadowYin-Yang, The problem is that you *can* lose elasticity in your breasts if you bind every day. It's up to you if that would be bad or not. This means sagging and not able to hold their shape as well (something that happens naturally with age, too).
I would speak to a doctor about it, especially if you're not transsexual.
Wearing a sports' bra - where it doesn't compress so much as hold in place is likely harmless.
However, have you considered "wireless" bras ? I find sports' bras don't offer enough support (unless they're very tight - bringing you back to the "binding every day" issues), but many "wireless" ones are just as comfortable (if not more so) and offer more in the way of support. I would never wear an underwire every day - "wireless" bras are great and really comfortable if that's what you're looking for.
@MagiFox, I would guess it depends, person-to-person, what "best" would be. You might try a 32A, if possible, and layer it over the usual one - and see if it's not too tight as to be uncomfortable. Just try things out and see what works best.
For colour, nude is the "best" - since it's going to be most invisible under most colours. White under white actually tends to look *bad* - you want nude under white or the white under white will actually show up in a bad way. You can't go wrong with nude, although wearing black under black or something would likely be alright unless it wasn't fully opaque.