tamiya painting instructions

I'd suspect that it means to mix the green and flat green and then paint the parts with the resulting color. The manufacturers sometimes do that when they want a color slightly lighter or darker than one of their "Standard" colors.

In the case of Tamiya paints their green and flat green are virtually the same shade though, so I'm not sure what they are trying to accomplish unless it's a sort of semi-gloss (not quite gloss, not quite flat) finish.

that's what it is Scott... I saw that on one of my tamiya kits I built, it wanted flat black plus gloss black... I finally figured out it was satin they were trying to accomplish...

Ders... pay attention too... there should be a number after a colon right after the paint color. i.e. XF-4:1 + X-8:2 ... the number behind the semi colon gives you the ratio of one color to the other... so there we have a 1:2 ration... 1 drop to 2 drops however you wanna measure it... thats what will give you the right shade/right gloss or dullness when mixing...