How do you make real fire green, purple or blue?

Answer 1

Essentially, what you need to do is to use a flame coloring agent which will emit the desired colored light when it is heated in the flame.
Some colors are easy to obtain, for example, yellow using Sodium compounds (ex. NaCl).
Other colors are more difficult since they are easily masked by stronger colors, for example, purple using Potassium compounds (ex. KCl).

This site explains many of the principles at work and lists compounds you might try (along with pictures of various flame tests),
http://www.amazingrust.com/Experiments/how_to/Flame_Test.html

And here it explains the underlying principle at work, spectroscopy,
http://www.amazingrust.com/Experiments/background_knowledge/Spectroscopy.html

Answer 2

Green: add copper sulfate or sodium borate
Purple: add potassium chloride
Blue: add cupric chloride

Answer 3

I don't know which ones exactly but by burning ions of different metals.

Answer 4

to change the color of fire you use different types of chemicals [elements]

Answer 5

Fireworks use different metals.