The colors.json file does not allow capital letters.
When you do put them in they are not registered as a capital letter but as a normal letter.

I was told that this issue was supposed to be fixed, however I have not yet been able to get it working with the latest snapshot.

Input would be "[Admin]" output is "[admin]"

Thanks for your time :)

Two different suggestions:

1.) remove .toLowerCase() and make the user pay attention for lower case color codes if possible
2.) add a second file roleprefix.json for use as %toproleprefix% in config.yml

Example for 2.:
Role: Admin
Roleprefix: A
Rolecolor: &c
Output: %toprolecolor%%toproleprefix% &r● &b%message%

Works. Good job!