An On-Axis Image Point
Now let's trace some light on the topic of chromatic aberration of a lens.
Using our canonical double Gauss lens, I've plotted the shape of the best single image point this lens can form while varying the wavelengths from blue to red. That image point is in the center of the camera sensor. Restricting the image field to this single angle highlights the degrading effects of color, although some constant degradation is due to spherical aberration. The off-axis image points can also be studied (and studied they are by the lens designer) but those results are further corrupted by other types of off-axis aberrations and tend to mask the chromatic effect we're highlighting here.
You can see the chromatic aberration animation by clicking here.