I saw this little engine many times in the early 1970's at Yeovil. The photo at http://railphotoprints.uk/p852530460/h63ED4264#h63ed4264 is a fairly good representation of how it looked close to the end of its life.
It was a very dirty faded flat matte pale green. I've seen other Ruston industrial locos in the same colour, though in a better state (e.g. at Radstock in the 1970's number 20 or 24)
I strongly suspect it was never repainted from new. It wasn't olive, it wasn't BR green. The yellow on the bonnet was almost certainly a locally applied DIY job with whatever cheap yellow paint was available - it was faded to dull off-white, with rust stripes.
The end of the loco came because it was rusted so badly the roof fell off in ~1972. Rumour had it that it was used for a few days roofless before health and safety kicked in. It sat at Yeovil Junction for nearly three years wrapped in a tarpaulin before it was finally scrapped. I've read somewhere that it was scrapped in 1972 - thats clearly wrong, it was still laid up at Yeovil in 1974