I'm not sure I understand what you want to do exactly.:)
You can just read the less file and see what colours have been applied. If the colours have been defined as variables (usually at the top of the stylesheet) then you could easily edit them as required. Or is it that you want to know what a hex colour looks like? You could just highlight the elements in the live page that you are interested in the using Firebug (or developer tools) and you will see the code for each element.
I guess I don't really understand what you want to do