That's OK, my apologies for going into some heavy stuff fairly quickly.
Primary lateral colour ( C2 ) is a simple variation of the image scale, where typically the red image is bigger than the green , and the blue image is smaller.
However in most well-optimised lenses, particularly wide angles, there are three contributions to the overall lateral colour which are mixed up :
1. Primary lateral colour ( a small amount, balancing no.3 )
2. Secondary variation of image scale, which is a bit like secondary longitudinal colour
3. Chromatic variation of (Seidel) distortion
Because of the different field-dependence, it's typical that No.3 above comes in quickly near the corners and reverses the order of red/gree/blue. The Laowa is a typical example. Colour is well controlled over about 3/4 of the field then takes a nosedive in the corners. Fortunately a lot of this is correctable.
If you look at a couple of wide angles in DXOMark, and check chromatic aberration > profiles, you will see this behaviour.
