Because every wooden canoe is different, having a set of formulas that simply work seems impossible. The color of the old wood in each canoe/boat depends upon the wood's age, species, how its finish was maintained, the kinds of finishes applied over the years, its exposure to sun, moisture, salt, other chemicals, how it has been stripped and cleaned, and more. In addition, the color of new wood varies too, depending on species, age, length of time since milled, and exposure to sun, chemicals, etc. Thus the best approach is to custom match new wood to old wood. With a "standard" stain formulation, you might get lucky and get a match, but you're much more likely to do so if you custom match. There are no shortcuts in quality work.
A practical approach? Make stain boards and use them to begin the process. For example, If you often work with red cedar, white cedar and spruce, cut pieces of each that have color and grain similar to that which you most commonly use, and stain in sections with a variety of stain colors, labeling each color clearly. Using these stain boards as a guide, you'll still need to approach your final color artfully. Use a scrap from the new wood in your canoe and, judging from the stain board, try to get a color that closely matches the canoe's old wood. Even then, for a good match, you'll probably have to sneak up on the color by applying multiple layers of stain or by trying different stain mixes.
The other important thing to consider is the type of stain you use. You can get very different looks, and the approach can be significantly different when using pigment stains vs. aniline dyes vs. other staining methods. Collor can also be had by chemical treatment, such as ammonia fuming for oak or potassium dichromate treatment of mahogany. These treatments aren't colors applied to the wood; they change the wood's color by changing its chemistry.
At Assembly a couple of years ago, Chris Pearson did a demonstration about carefully approaching color matches using dyes. His presentation drew a huge crowd and people asked lots of questions. His work, Zack Smith's and the work of some others here shows that a careful, thoughful approach can produce outstanding results.
In short, there just can't be a one-size-fits-all formula if you really want a quality color match. Of course you can just slather on stain and make wood look darker and colored, but it sounds like you want to do better than that... and you can with thoughtfulness and care. With practice, and you already have a lot, Howie, you can get good at this quickly.
