Treesner suggested a solvent-based dye for their garage floor, however, this is not ideal as any spilled solvents may damage the sealer and displace the added pigment. The sealers designed for solvent-based pigments are either xylene or acetone-borne acrylic and will be damaged by mineral spirits, acetone, xylene, gasoline, etc.
The best practice for a garage floor depends on whether the concrete is freshly poured or already has damage from prior use.
For freshly poured concrete, light sanding with a swing buffer and an application of a concrete specific polyurethane can preserve a natural concrete look, and is incredibly durable. Application is relatively easy and can be DIY installed, especially with the help of a friend.
If your concrete slab is already damaged by oil spills or other contaminants, an opaque epoxy system is a better idea. Most commercial epoxy systems have either epoxy flake or quartz sand broadcast to rejection to increase durability and slip resistance. The systems that are purchased at home depot or other big box retail have the flake as an aesthetic input only, and will be quite slippery in standing water conditions.
While slightly more difficult to DIY, the industry standard for durable garage flooring is a broadcast system.
This would be:
Basecoat of 100% solids epoxy with sand or flake broadcast into it for rejection.
Topcoat of concrete specific polyurethane. Depending on the viscosity of poly it may take 2-3 coats to get consistent coverage. The poly can be clear or colored depending on the aesthetic goal.
While polyaspartic is often used in commercial systems, it has a really fast cure time and is very difficult to DIY install. It's also generally quite viscous which makes it more difficult to avoid roller lines, etc. I'd avoid it for a DIY install.
In most large cities there will be a commercial Sherwin Williams that sells decent quality epoxy products. 100% solids epoxy base coat and high solids poly topcoat are the keys for a long-lasting install. Other brands to look for are Sika and Westcoat. Both will be sold through distributors.
Torginol is the main manufacturer of color flakes and will sell individuals 40lb boxes. Most 2 car garages will require 2-3 boxes. Smaller flake is more in style currently--1/8th" or less. I used 2.5 boxes in my 600 sq. ft. garage.
Heres a pic of my garage. I've spilled solvents, gear oil, gasoline, etc on the floor and it wipes right up without any staining.
Here's more info about commercial epoxy floor systems vs big box retail systems. Depending on the amount of abuse the floor will see, it can easily be worth the extra $800 in materials to install a proper commercial-style system. Big box retail systems are quite prone to flaking and failure, especially with DIY concrete prep techniques.
Jeremy