Wood dyes (as opposed to pigment stains) are beautiful products because they have very small colorants that impart a very even color to stained wood. This is because the dyes penetrate deeply, leaving a beautiful clarity to the colored wood. Pigments stains, on the other hand, are made with relatively large pigment granules and they color by the pigments lodging in the grain of the wood and in surface roughness. This is why pigment stains are so effective at highlighting the grain. Because pigment stains sit on top of the wood, they tend to muddy its appearance more so than dyes (the ultimate in this category are the filler stains often used on mahogany runabouts- these are often glommed on the wood leaving a hideously muddy appearance, in my humble opinion!).
Dyes are either dissolved in water or alcohol. Water as a solvent makes dyes that are easier to control; dyes in alcohol dry very fast, but don't raise the grain as water does. Here's the big potential problem, though: as pretty as dyes are, almost all dye products warn against them being non-color-fast when exposed to ultraviolet radiation. Behlen's Solar-Lux is supposedly more light-stable (hence the name). TransTint and TransFast dyes specifically warn about using them in high-UV environments, even indoors. Most pigment-based stains are much more light-tolerant.
I have asked manufacturers about the use of dyes under UV-shielded spar varnishes, and have gotten only equivocal answers. Thus, dye colors may not be permanent under long-term exposure to UV radiation. On the other hand, our canoes generally are not left baking in the sun for great lengths of time like the decking and trim of Florida yachts, and our canoes are covered in UV-shielded varnish. So dyes are probably a good risk, especially given their ease of use and excellent coloring properties. If they aren't permanent on our stained ribs, I wonder whether they will simply fade to a lighter version of the same tone, or whether they will color-shift. Mike, let us know if your new ribs turn purple someday... maybe you'll start a new avant-garde trend in "designer" canoes!
Michael