I love the coloring box + bar thing, guess it's one of those perks unity comes with or did you code it yourself (I'd like to see base code if it's the latter)?
The color picker is free asset of unity, and truthfully since only pro version has access to source code, i can't say much about how it's work, but i believe if you want colorBox(only) there is three script on githtub for unity or i believe since i never checked because i was looking for something akin to current one (but as unity supports gradients it uses gradient and the only problem that might come is to convert position of slider to color (Also all UI elements for are unity standard ones, the others besides are part of asset i use). Also if you search for general source code of colorPicker i believe there should be at least few projects on githtub written in different languages so you might check it)
ps. i also consider as good asset this colorPicker and might even buy pro version not because i would want to look into source but because to support author, since the quality of others colorPickers on assetStore is somewhat disappointing.
ps2. Any one has and idea for sexy theme for my game (i need only a general idea how it should looks like, and i would make them myself)
edit: Here the link for unity free source code for colorPicker http://forum.unity3d.com/threads/color-picker.267043/
and it's show rgb value like you saw, if you want to use hex just use and input field besides icon to open colorPicker (and the current one will not use unless i change color picker to these one from repo since it's possible that i might do that since i would prefer some modification of color picker.
edit2: Must say that i changed colorPicker to version from githtub since it allows me to use hex values and i can start with chosen color (which is the current color in the case of current hairstyles it's single color but for other items/hairstyles it will use up to 5 different colors).
Also anyone looked towards files since almost all resources used by game are loaded from external data, so for example i have two images from WM as starting screen but anyone can change them towards they own, also it use db to configure game data so you might check how it's currently look db schema).