I dressed as a pirate today. So I will bring tips on changing the color of you beard. I wanted to dye by beard black so that I would look more "piratery". The process is actually fairly simple, though I think it would be a little tough to pull off a beard that would pass close inspection. My beard looks fine from several steps away, but once you get within arms length it starts to look like it was colored. I suspect that under harsh lights it would also not pass muster. My beard was a nice shiny back and stands out under light.
I used Just for Men "Jet Black". Which given my coloration really looks weird (Hint: I am a white boy.) I followed the directions well enough, though I did not wear gloves like they told me to. That was a mistake. I should have, because the tips of my fingers were stained with the bread dye. If you plan on changing your color multiple times over a period of time, invest in some surgical gloves so that you will have them on hand when necessary.
Also cover your work area well. When I was brushing the color in with the brush provided, specks ended up on the sink. I looked for them last night, but I missed them and now my sink has a few small dots that will not come off. Leave no trace is the way to go in this case.
I would start with the hair that will be the hardest to color, either because they will require more dye or because the area is a little thinner. For me it was the top part of the beard, the mustache, and the soul patch. These areas were not the same color as the rest of my beard and were thinner in some cases. Some of the hair actually lacked color. The reason why I would start with these areas is because the longer you leave the dye on, the darker the hair is going to get. Secondly, you want to spend your time on these areas to make sure you don't get the dye on the skin you can see below it.
I would go for a lighter color than your hair because you can always reapply to make darker, instead of trying to make the hair lighter by washing the dye out earlier.
Most importantly, I would like to point out, that for some reason beards, are not all one color. They are a mix of tints. If you are going to do a job that pasts muster on close inspection, you probably should have a range of colors that you either apply selectively to certain areas to provide highlights or actually mix in to lighten a mix for a certain area. I know personally my mustache and soul patch could have used some brownish tints. You might even experiment with applying the color with small paintbrushes to get a better-looking beard.
DO NOT expect to be able to pull of a radical change of the color of your bread in broad daylight with our some sophisticated work on your part.
Update: Spent some time with several friends and they noticed that my beard was much darker than it was last time they saw me, but none of them reached the conclusion that I had dyed my beard until I told them. Even when my beard was many times darker than my actual hair color!! Bottom line: If you need to change the color of your bread for personal reasons and not to evade authorities, just for men work great. Otherwise you will have to put more work in making your bread look natural, in my opinion.