I know that many of you ladies--myself included--are inclined to skip wearing a base coat when you're painting your nails. I get it. It's an added layer, which means more time waiting for your nails to dry and more bottles cluttering up your space. But wearing a base coat is a lot more important than you may think.A couple years ago, I was really into wearing red nail polish. I never used a base coat and soon found that my nails had an ugly yellow tint to them. Not only was this disgusting, but it also made it difficult to wear pretty sheer pink polishes, as the yellow would show through a bit (sorry if that's TMI).
You can always simply bleach your nails, but that's horrible for your skin. If you've got yellowing nails, try rubbing lemon juice on the base of the nail (maybe for five minutes daily for a week) and the yellow hue should disappear. That said, it's really best to avoid the issue entirely.
The best basecoat I've found to date is Seche Base. It's a ridge filling basecoat, meaning that it smooths out all the little imperfections you may have, and it's main redeeming factor is that it's slightly shimmery. And I do love shimmer. It's actually pretty enough to wear on its own; just throw a top coat over it. It also adds a tid bit of shimmer to any color you wear over it.
You can buy Seche Base at drugstore.com (which, by the way, carries great products for way cheaper than actual drugstores) for $6.99.