On the frontend, the typography style overrides the color of the .btn styling.
See the image for an example. The button on the right is a input[type=submit].btn. On the left, it's a[href].btn. Also, on hover, the button on the left gets the color change (which is consistent with the submit) but ALSO gets an underline.
I'm using greek yogurt now, and I realize this is the theme's "fault". Maybe the .btn color and text-decoration should be "!important"?
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I have verified this bug still exists in the current version of concrete5.