Anyone know the paint colour to respray an Apple II case

You might want to check the term RetroBrite. Where basically take H202 and UV light and reverse the aging color back. Slower is better.

The basic color is commonly marketed as
"Sand" or a variant. I usually use Rustoleum
"Gloss Sand" and cut it 50% with reducer and
shoot it with a commercial spray gun. The
color is a dead match. you can probably get
simialr results with rattle-can paint of the
same brand.

If you lay the cots on thin, they won't be
as "shiny" and so will retain a semi-gloss
finish similar to the factory.

Also Rustoleum paints don't fade as badly
from UV light.