Because of the high quality of the 0.8mm kangaroo leather and tightness of the nap (the fibrous/suede) on grain side is so tight that it can be hard to tell the difference.
With the hide that I have at the moment the dark side is the shiny side and the lighter side the suede side.
This can vary from hide to hide. So I went to take a picture to show a customer the difference and I noticed that the white marker was more obvious on shiny side because it stayed on the surface and harder to see on the suede side because it was absorbed straight away. This gave me the idea of a droplet of water which beads on the shiny side and is absorbed straight away on the suede side.
The suede side is the side that you apply honing compound to. Then wipe your blade off on a clean cloth (don't pinch the between your fingers to do this because the blade can bite you through the cloth, learn from my mistake : ) ) now you can give it a final buff on the shiny side.