Achromatic and apochromatic lenses have already been mentioned. Chromatic aberration results in different wavelengths being focused on different planes. It should be clear that with achromatic lenses, extreme wavelengths will not be in focus. This does not so much produce spurious colors as simply some very slight fuzziness. Apochromatic lenses are the best, since all visible wavelengths will be in focus.
Apochromatic lenses require many glass elements, and therefore are normally very expensive.
The reason that blue and green filters are provided with our less expensive microscopes is that by filtering out the extreme visible wavelengths, chromatic abberation is eliminated. Notice also that the curves below are not perfectly symmetrical. That is because, even with the best manufacturing procedures, there is variation from objective to objective. Curvature of field means that if the center of the field of view is in focus, the outer edges will not be. That is, with the center in focus, the outer edges will be blurry.