AngularJS Directive Value

I have an AngularJS directive. My directive is restricted to be used as an attribute. However, I want to get the value of the attribute. Currently, I have my attribute defined as:

angular.module('myDirectives.color', [])
    .directive('setColor', function () {
        return {
            retrict: 'A',
            link: {
                pre: function () {
                    console.log('color is: ');
                }
            }
        };
    })
;

I use the attribute in the following manner:

<button type="button" set-color="blue">Blue</button>
<button type="button" set-color="yellow">Yellow</button>

I know that my directive is being used because I see 'color is: ' However, I can't figure out how to make it display 'blue' or 'yellow' at the end of that console statement. I want to get that value so I can do a conditional processing. How do I get the value of the attribute?

Thank you!