What's the difference between Brown filters, and White filters?

In earlier times, most white paper filters were whitened with bleach. Not only was this not very friendly to the environment, the bleach imparted nasty flavor overtones to the paper. Today, most white paper filters are whitened with oxygen. Oxygen whitening is much more friendly to the environment, and imparts no taste to the filter. Brown filters are simply unwhitened. Your choice, but oxygen whitened filters are usually less expensive.