Wow, I'm a bit surprised how that suggested alternate green looks so visually identical. As for the Illiad chip, online here it looks fine compared to those found in the British Aviation Colours book and the readings done by Nick Millman -his actually looks a tad more brownish.
I tried something digital as I don't have access to that many Vallejo paints. I made some RGB valu chips from Harold's first post with the spoons. Results show a 50% warm grey (that was why I suggested brown, but a red would also work) combined with 50% of DK Green from Vallejo 71.324 give the colour value of the Illiad swatch.
Alternately, if wanting to add just a 10% paint to 90% of the Vallejo green, then the required additive is a deep bluish purple.
Mixes were done using this online blender:
https://meyerweb.com/eric/tools/color-blend/#000000:626C3C:9:rgbd
regards,
Jack