Thanks Andi, just followed your advice and thats has helped to remove the slightly radioactive green I had before !
Do I take it from your advice that most greens should be mixed from primary colours ?
It's a big subject Gordon, and one that you couldn't do justice to in a few short words. But there are some guidlines worth mentioning.
Use "tube" greens only as a tinting medium and try and create your Greens from Blues and Yellows.
For instance if you want a sunny day you would pick a bright yellow such as Cad' [high chroma] Yellow - using only this and mixing it with a selection of blues [Cerulean,Cobalt, Ultra',Indigo,Prussian] would give you a range of "summer" sunlit greens taking in brightly lit through to a deep shadow green - If you were to start with a dull Ochre - [low chroma] Yellow this will give you a selection of "winter" greens within the same sort of light range.
Conversely starting with a bright blue and using all your Yellows [Lemon,Cad',Gamboge,Ochre,Cad'Orange] will give you a similar range of light effects but on a rainy or overcast day..................... etc etc!
It is even possible to represent quite accurately the time of year [season] and even the time of day!!!!!
Whilst "giving it large" during lectures I'd pick on a student and identify their birthday with colour using these theories, but the really "twilight" factor was once they were shown it; 90% of them would exclaim that that was their favourite colour on the chart?? - Never really worked out the science behind that but I deeply suspect we were well into the realms of Synaesthesia [of which I'm a strong synaesthesiat].
Here's a poor shot of me I managed to find at the chalkface explaining this exact phenomena to a bunch of disinterested pre-grads', you should be able to see what's going on from the pic' as it's fairly obvious that we're working at a retro engineered level of colour identification, it's when you overlay it with a bit of theory, psychology and philosophy that it gets proper interesting.
Gordon it's a massive subject [just this single portion alone would run into several double period lectures] but I hope it's wet your appetite or at least give you cause to think on?
Ps - in true terms a tint is a hue[colour] plus white. Where as a shade is a hue plus black - but of course you NEVER put black into a painting!! .................... I could go on!