Francois Brunet / Epicerie Boulud defined layer Croissants??

Ignore the coloured layer and just make croissants. Make many. Keep making them until you're happy. This will take several iterations. Quick diagnostics: If they come out of the oven soggy and swimming in butter then they're under proved. If they come out overly "bready" then overproofed and/or worked while too warm. You need to find the sweet-spot. Work in the coolest place in your kitchen if at all possible. If your fridge isn't up to it, then use your freezer for the dough between laminations, but use a timer... 25 minutes...

then add the final coloured layer. It's just one layer - not even laminated in with the butter, so in some ways a bit of a cheat, but it's very effective. When you get to this stage, the key is to look for "bake stable" food colouring. This means that it won't change colour/fade in the oven. Look for non-azo colouring if you're also into that sort of thing too.

Back to croissants. Look here for txfarmer's pages. Read them. Read them again. Make croissants. Go back and read more.

You get the drift? Basically get good as making basic croissants before going for the coloured layer - by that time you might find that the coloured layer is nothing more than a novelty and your family/friends/customers will be mighty glad of your fine hand-made croissants! Watch this video (for some fun, if nothing else): https://www.youtube.com/watch?v=L36OiPWmOL4 The tip I got from that video was to use a brush to remove as much flour as possible before folding.

My croissant dough is a basic sweet dough at about 58% hydration. 10% sugar and 50/50 milk/water. I don't put any egg into my croissant dough. I make the dough, let it rest a short while, then into the fridge overnight before I start rolling. You don't need a hand-squirter for the egg wash, a nice soft pastry brush is fine - but when I get to the stage of making more than 2 trays at a time I think I'll move over to the sprayer... (A good shiny egg wash is one egg, one egg yolk and a pinch of salt - mix, leave for 10 minutes before using, but just an egg beaten up is fine to start with)

On the butter front - I'm in the UK where we have a minimum of 80% fat in our butter by law. Same for Europe I think. (French) President butter has 82% fat in it & costs twice as much. The stuff I use has more as I get it directly off a farm via the wholesalers - it's very dry and stays hard, so needs a lot of work while cold to soften it. I use unsalted butter too.

Enjoy,

-Gordon

I haven't made too many croissants yet, mainly because they are rich beyond belief and I consume a lot of bread (and beer!) as it is.  May I add to what Gordon states...

also cross reference the entry by Hanseata on her croissant journey. Between that and the fabulous txfarmer output, it is a great pair of reference points.  

Cold work surface, cold rolling pin. I just inherited a marble rolling pin which I intend to place in the freezer for the next go-round too.

it is just as easy, and probably more traditional to brush on egg wash as to spray it on.  That's for someone who makes hundreds, not a dozen or so.  

Minor dough development as the laminating of layers will further develop gluten and you surely do not want to overdevelop the gluten, else you will wind up with an elastic dough.

constantly brush fresh flour off the dough, both sides.  Don't want that raw flour to interfere with layers adhering to one another.

final proof, covered, until very jiggly, when the baking pan/jelly roll pan is shaken.

three laminated folds.  Punto final. That will give the dough the traditional 27 layers.  Return to refrigerator between folds.

what we see these guys do is accomplished in professional labs.  Almost all of us here on TFL work in home kitchens and have to make some adjustments for that.

lots of other hints, but you'll have enough here already to give a good head start.