Don, I would suggest for lighter mixtures to always try just white first. It works well for many mixed colours, particularly if you are not lightening excessively.
If it doesn't work - and you can be sure it won't in all cases
- then try using white and something else.
For shadows, try using either grey mixed into the base colour or a mixing complement to make the initial colour (what painters would call the halftone) and then try adding a little black to that; just a small amount, you only need a little too much for something to go too dark too quickly.
It's worth mentioning that personal taste drives a lot of colour use in the hobby and realistic colour that's very similar to how things might look in the real world is simply not to everyone's taste - some people prefer brighter, more vivid colour, some people prefer much duller results (e.g. Bob Knee and Kostas Kariotelis at each end of the spectrum). Somewhere in the middle is where natural colour lies and it's where the bulk of the work of accomplished painters lies (e.g. Bill Horan, Greg DiFranco, Mike Good).
housecarl said:
Don, I use a component / complimentary colour. Green is made from blue and yellow.
Green could be said to be largely green (
see here). Only dull greens actually have a significant blue and yellow component, as in
Chromium Oxide Green for example.
With complements it's important to understand that visual complements, as shown by the facing colours on a proper colour wheel (one including cyan and magenta), do not tell us what
will work in mixing. It suggests what
might work, but practical experience shows time and again that in reality complementary pairs are very often not opposite in hue.
housecarl said:
So to darken more blue, lighten more yellow. This is an over simplified version, but hoppefuly you get my drift.
Lightening greens with more yellow and darkening them with more blue makes bluer shadows and yellower highlights, which is fine
if it's what you want but it's not the way green will tend to look IRL. Highlights and shadows are, generally speaking, the same hue as what we'd think of as the base colour (the local colour in painting parlance).
The visual complement of green is magenta or thereabouts but the
mixing complement of something is whatever works... in actual fact many green paints are actually neutralised best by violets, strange as it sounds.
Einion