Changing Color of Theme – Is it easy?

Hi. i would like a little help to change the colour of my blog’s theme, i.e. background, text colour, links – almost everything. Is it just a case of downloading the stylesheet and changing the color codes then uploading it again? Below is my stylesheet, I think I can identify the colors ok. Is there anything else I need to do, this is quite new to me and I don’t want to make any mistakes. This is my website

http://www.buildyourlifetoorder.com/

and basically I would like a white background, dark text, dark border. Thanks for your help.

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