3 questions about colour television

[Rinehart]

If anyone can answer these, I would be most grateful:
The NTSC monochrome standard ran at 30 fps; when colour was introduced, it was reduced to 29.97 fps, a reduction of 0.1%. Why did it have to be reduced at all, and why by that amount?
What exactly is the "colour burst"? Is it a kind of synchronizing signal?
What were shadow masks made from? Presumably the material had a low coefficient of thermal expansion, but were there other considerations as well?