I applied panel lining and markings.
For panel lining, I used Real Touch Markers in brown and gray 3. I used Real Brown on the orange and brown armor parts, and Gray 3 on the gray parts.
After roughly applying the panel lining, I used a blending pen, Mr. Thinner, and 1000 grit sandpaper to refine the edges. This resulted in sharp panel lining.
I didn't use enamel paint because the parts weren't coated with paint this time, and I wanted to prevent any potential cracking of the parts.
This is what it looks like with the panel lining applied to the entire model. The markings are not decals, but from the old HG S

I started playing Heine Guf as a break (Part 5) | ヘイカユウジ's Gunpla works