Copied from LB&SCR.org website.
"In the Stroudley and R.J. Billinton period we have the famous Stroudley "Improved Engine Green", actually a golden yellow ochre. This colour has given rise to numerous disputes. There are theories that he was colour-blind or that to get the board's approval he described it as: "an Improvement on (the existing) Engine Green" - hence "Improved Engine Green". Stroudley had used the yellow ochre livery on the Highland Railway previously, so the answer probably lies in their minute books. In H.J. Campbell Cornwall's book, he suggests that the "Improved Engine Green" also known as "Scotch Green", referred to the goods colour which was a shade darker than that used by Craven."
So that clears that one up then

Max.