Hello Rod,
Good to see someone else painting Japanese.
I'll try and help you as much as I can. My Japanese forces which I'm painting up are for the Solomons, PNG etc. My SNLF will be painted diffently for the South-West Pacific as oppose to your at Tarawa.
From Osprey "The Japanese Army 1931-45 (2) 1942-45" Plate E 3 shows a Acting Leading Seaman, 7th Sasebo SNLF; Tarawa Atoll, Gilbert islands, autumn 1943. In the description is goes onto say this" This hei-cho of Rear-Adm. Shibasaki's garrison, during the preparations to defend the island, is hardly distinguishable from an Army soldier apart from the yellow anchor on his field cap; the earlier distinctive 'sea green' colour of NLF uniforms was now giving way to a wide range of khaki and green shades. The rank patch on his right sleeve is of the series introduced in November 1942. Under the camouflage netting of his 1932 pattern steel helmet can be seen the embossed naval anchor badge. His 'landing shoes' (ankle boots) are black; as normal worn by naval infantry instead of army brown; is basic belt equipment is of the standard brown leather type, however. Small arms were also common to Army and Navay troops.
I've the Osprey Japanese Special Naval Landing Forces as well. Most of the uniform plates are from Reenactors, but it gives you a good sense of the early and later uniform.
If you are after my painting opinion for a girl who has been painting khaki for the better part of a year on many a different country I'd go for a khaki/yellow green mix. I'm heading down the road for using the Russian Green with a mix of colours to see if I can achieve the 'sea green look for the early SNLF for the Solomons.
What figures are you using?
Best of luck,
Helen