Adding support for hex colors

[sugaaloop]

Hi! Not sure if you have any interest, I came across a use case for adding colors dynamically from gulp into sass (white-labeling an application) and wanted to see what you thoughts were for injecting hex colors. I needed the colors available in both sass and javascript and didn't want to define them twice.

I know it's a little hacky, but I couldn't think of a cleaner way to identify a hex color in JS.

[squatto]

I just found this PR because I need the exact same thing: externally-defined color variables in a white labeled application. This would be great!

[squatto]

@sugaaloop for now you could use this: https://github.com/giowe/gulp-sass-vars - it would be simple to export a JS object from a file so that you could dynamically set your variables.

[sugaaloop]

@squatto i'm currently using my "fork". gulp-sass-vars is using parse-sass-value, which looks like exactly what we're looking for. i might check it out, but for now this PR is working well enough.