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How do I get brilliant color without over-exposing? - understanding exposure peterson

I am new to the SLR world and have fun with my new Canon Rebel XTi. I feel comfortable with manual settings, but I can not color the way you want. Or am I over-exposed and clean bright colors or less exposure, and color looks sad. I wonder the book "Understanding Exposure by Bryan Peterson helped tons, but I wonder whether a better book to help me with my problem. Shutter speed is my mistake? ISO? Aperture? All of the above? Advice or instructions will much appreciated!