Retarder helps with blotchy spots (and with grain raising in some dyes) same is working in a cool place to slow down the solvents evaporation, spraying its a great help too, i dont always use a real sprayer (sometimes i do stuff at night and the compressor make too much noise) i use a spray bottle with my anilines, its the kind used for parfumes so delivers a fine mist, i find it great for shading, something impossible to do right away with a rag, a little practice and you can obtain an even coat and eventually darken lighter spots only. Many people say that water dyes cant be sprayed... it works for me so whichever kind you use its worth a try (the average spray bottle its a little more "rough" but works too, but you have to remember to wipe the nozzle from drops every couple of squirts or youll find a nice even misted area with a few bigh drops in it).
If you dont have a spray gun and dont want to (or can) use the spray bottle give a look at the disposable Preval Spray Units, they are pretty inexpensive for the one-time jobs.
Remember that dyes do look more blotchy when wet, when they dry the richer part gets more absorbed and lighten.
Some wood conditioners work with alcohool based dyes, not with water based and solar-lux instructions say to go on bare wood, other ways to even out the color are more coats (this darkens the overall tone so thats to take in account), colorwashing: going on the dye with its own solvent (reducer for solar-lux) and practically washing off the color, then reapplying and so on, going after the dye with a compatable pigment stain: it evens out things adding in some cases an interesting "depth" effect (nice on maple), you can sort of obtain a similar thing dyeing (sp?) the epoxy if you precoat before laminating, the last way i know of (and the best one for me so far) its to saturate the wood with the dye solvent before applying the dye, the concept is that since blotchyness its due to different absorption the pre-saturation of pure solvent helps leveling the differences.

If you want darker colours try to avoid using black, its really a matter of small quantities and can reduce the vibrancy of the original color, if it can make more sense: it adds to the greysh tones dulling the others. If you can use multiple coats or mix (or overcoat) with a darker shade of the color you are using.
If you use black then my suggestion its to prepare a batch with black and your original tone, then use that mix to finetune more gradually the tone of a new batch of dye that youll actually use. keep in mind the quantities because its easy to end with more than you need, although if you get into dyes youll find yourself with 20 different tones that youll routinely mix and match, so they are never wasted.

There is another way to get a darker tone that with some woods gives a real cool effect and consists in using a black dye(or dark mix) on bare wood then sand it off until only the grain keeps it and then going on with the tone choice dye. Thats even the way to obtain shadings if you cant spray.

(if you want, check with people that works with guitars, violins and such, they know a pile of stuff about dyes and have tons of tricks and recipes, specially the older guys)

: I dyed the kayak today. It's Solar Lux Blood Red with 10% retarder put on by
: hand. I've never really used a dark stain or dye like this and it was
: harder than I supposed it was going to be. It's not exactly blotchy, but I
: can tell it was hand applied. I can live with it, because it looks very
: cool. I wouldn't mind it slightly darker and I think if I do this again,
: I'm going to mix about 70/30 Blood Red/Black.
: What I'm wondering is will the color darken if I add a second coat? Will the
: epoxy darken it like it does with cedar?