Your not going to get an answer to this, there is no magic wand you can use to change what your asking without working it out yourself, or at the very least supplying some actual code with your question.
To change the CSS in a back-end option page you can use the Options API, http://codex.wordpress.org/Options_API, or write a custom CSS file and include it in your header.
As Mark already mentioned there is a color picker that comes with WordPress that you can use to fill in your custom field options with color values.