Recolouring Button Background from Skin

I'm trying to change the way the buttons look for my application.

I found a tutorial which suggests that one creates a new GUISkin and updates that, and I do like that as a solution.

Now I'm trying to change the colour of the button. I am okay with the style of the default one, I just want to change the background colour to something else. Is there a clean way of doing this?

I've searched for this a bit and the solutions I found involve either:

1) Changing the colour in the OnGUI() part of the script

or

2) Obtaining the default buttons and recolouring them in a graphics program.

Is there a way of doing this from inside the Skin? In a similar manner to changing the font colour ?