Give yourself a kindergarten color refresher course: Red, yellow and blue are primary colors; red and yellow make orange; yellow and blue make green; blue and red make purple - and altogether they make a gross grayish, reddish brown.
Step2
Update your palette: Burnt sienna is reddish brown, raw umber is rich, dark brown.
Step3
Decide on your stain base: For oil, use mineral spirits; for water, boiling water.
Step4
Decide which colors you will need to achieve the tint you want.
Step5
Buy or borrow whatever you're missing (if you've got a base and chrome yellow but you want an olive green stain, get some black before you start mixing).
Step6
Start with a small amount of your base.
Step7
Add color drop by drop, stirring well after each addition and alternating if you're adding more than one color. (For example, to make green, start with base, and add blue and yellow alternately.)
Step8
Dab onto wood, let sit, and wipe off to test.
Tips & Warnings
Matching the completely bizarre color you mixed yourself is even harder than matching a commercial stain chip, so remember what you've done (writing it down is not a bad idea). Once you've got the color you want, mix as much as you think you'll need to finish the job - and if your project will stretch over a few days, cover with plastic wrap and a well-fitting lid.
Almost anything can be turned into a stain; one of the easiest stains is household dye mixed with boiling water.
Different brands of stain can be mixed successfully, but oil and water do not mix. If you've got both water- and oil-based colors, remember to check the labels before you mix the colors.
Make sure to take into consideration what you're staining. Your result will vary not only according to the color of the wood you're staining but also with its absorbency. Pine, for example, will show color much more intensely than will teak or walnut, not only because it's lighter but because it's a softwood.