Add [colorize modifier

Adds an option to colorize textures with an modifier by using HEX-Colors in RGBA-format.
![colorize](https://cloud.githubusercontent.com/assets/3742497/4501786/8577fd60-4ab5-11e4-8fb3-6b58425d9c30.png)

Why not keep it like this?
<pre>
ColorString
--------------
</pre>