[1sleeper]

Type 1 is plain old Portland and general purpose fine for most projects.
Type 2 is sulfate resistant. Many manufacturers don't have high levels of tricalcium aluminate so they can call their Portland type 1/2 (or type I/II).
Type III is ground finer (called blain, finer blain). This gives it more surface area and makes it set up faster. We call this "high early" cement for higher strength early on. It peters out quicker though not making the same ultimate strength as if you let it set slower.
Type IV is the opposite of typeIII. It sets slower gaining higher ultimate strength and reducing the heat generated. Called heat of hydration, hydration is the reaction that makes concrete get hard.
TypeV is very high resistance to sulfates. Used in parking structures and runways.
Any TYPE with an "A" after it means it has air entrainment to enhance freeze thaw durability.

The use of white over gray is strictly asthetic. To me, white might be too bright by itself. You could use a color with it to give it a nice shade. The colors are mostly mineral based so I can't see them harming anything. You can get lighter shades with white versus gray, just like a canvas.