Good advice ganamoha. I usually practice caution though I can have my irresponsible moments. Though I've never actually gone in deeper than I can handle. I've had a few experiences but never too intense. I guess I lack the will to get into it much.
Each chakra is associated with a vibration and color. This information should easily be found online for free. When meditating one will make the sound (vibration) of the chakra.
There's plenty of free information on the Internet but sadly it's not always correct. I'm not quite yet convinced on the rainbow colour theory yet. It's always best to find information from experienced people and I doubt most of the people on the Internet have had much experience. This reminds me of a Buddha quote.