The only issue I have with colorization is the colors in any given scene are arbitrary and may not reflect what the scene actually looked like.
Any given shade of gray can be represented by many, many different colors.
Absolutely. It can certainly be abused, and I've seen some poor examples. Some of the TMC stuff I've seen was ghastly.

I'm sure however that these guys probably did a fair amount of careful research on uniforms, vehicles and native foliage in the area. It's probably not an unreasonable approximation.
Of course, black and white is even farther from what the scene actually looked like. And even color film is only an approximation. It can't capture the full dynamic range of hue and shade that the human eye can. Certainly not the resolution.
But technical issues aside, I always have found well done colorized historical footage intriguing.