Chromatic aberration occurs because the lens is not focusing the different wavelengths onto the image sensor at the same point. The results are usually seen as a purple fringe on the image. The likelihood of chromatic aberration increases in high contrast situations and wide open aperture. To decrease the chances of chromatic aberration avoid high contrast situations if possible, if not then stop down your lens. Below are sample pictures taken with the Pentax DA 50mm F1.8, FA 50mm F1.4 and the D FA 50mm F2.8.
None of the Pentax 50mm lenses showed any measurable chromatic aberration in these tests. However, other sample photos (found later in this review) revealed that the FA 50mm F1.4 can exhibit noticeable purple fringing.