Fiebings is what I usually use as well. It's an alcohol-based dye. There are also some oil-based dyes out there that will work too. It's a bit tricky to dye something uniformly, so you may want to practice a bit before doing it on something you really care about. They make a pre-dye conditioner as well, if you're having problems getting a uniform color. Then it obviously needs a good finish over the leather.

One thing I've found is that dyeing leather evenly is very much a function of the leather itself. Different tanning processes and different qualities of leather will make a huge difference. Cheaper leathers take the dye in a splotchy manner. Or if you're dyeing something that's already made/assembled (like a shoe), it may have various compounds already on the leather that will inhibit the dye from penetrating evenly. Oils, waxes, anything like that can cause a dye to soak in unevenly.

What confused me is your mention of "cracks". I'm not sure what you mean by that. Also, you mentioned "layers". Dyes aren't applied in layers. It soaks into the leather; it doesn't sit on top in layers like paint. When dyeing leather, you want to avoid having to come back with a repeated application if possible. It is difficult to get a uniform color once the original application has soaked in and dried.