Since button color is part of post/page content (not templates or the framework), they do not change based on skin chosen. Have a look at the page –
Possible colors are listed there along with the code at the bottom of the page.
Pls use one of these colors – cyan, red, blue, orange, green, teal, black, pink when you supply color to the shortcode
[button color="blue" href="#" align="left" size="large"]My button[/button]
Also, nothing to do with buttons and just my suggestion –
To enhance the look of the website, you may want to take a shot at using a custom font as described in the post –