Theme Options Help: Change CSS colours

I’ve made a theme for my wordpress site and would like to have a theme options page to change the colours.

Link to site. (Don’t scroll too far down if you don’t like blood).

I’d like to be able to change all the blue elements to other colours. I guess I’d have to do something like

if colour-selection is red: link red css

But would it be possible to have an option to put in a hex colour and have it change the colours based on that?

I’ve tried looking online for answers but it appears my Google-fu is off today – can someone point me in the right direction?

Thanks very much!