Make mixing notice colors adjustable

[halirutan]

Summary

While the colors for notices are adjustable through their respective, e.g. $info-color, variables, their final appearance is a mix of hardcoded white. In dark schemes, the color is barely noticeable, and it reverses the contrast, i.e. dark text on a brighter background. Would it be possible to incorporate the fixed settings of #fff, the mix percentage, and the font color into easily accessible variables?

Motivation

Upfront, your theme is awesome to a degree that I can barely put into words. I'm using it on different sites for a long time. Until now, I worked on a clone of your repo where I adjusted the bits I needed. Last night, I gave the gem version a try and it seems I can incorporate all my changes into a main.scss without hacking any other sass file. The notices are the only thing that caught my eye which I'm not able to change without overwriting some of your code.

I believe for the general user, it's a noble goal to make your theme as adjustable as possible by setting simple variables instead of digging through the code. Using your gem version, I could reduce the work on my side from handling different branches of your repo to just using the gem making changes in one place. The color for notices should be a minor tweak from what I can see but I might not have the entire picture.

Drawbacks

Obviously a bit of work on your side and a headache from thinking about good variable names.