Update: So I found out how this plugin determines what the prefix tag is. Obviously, the majority of people who read this will probably know this already, but it's in the store-core.inc file.
PHP Code:
#define STORE_PREFIX "\x04[Store] \x01"
I believe that a simple inclusion of "<morecolors>" would allow for the inclusion of any color in the prefix. However, I really think the current method of defining it in the store-core.inc file should be changed, and converted into a CVAR that can be set up and changed at will, allowing for flexibility and the option of changing the tag color.
Some people might not want to have "[Store]" prefixed, like myself. I'd prefer "[STORE]". Some people may even want to add their clan tag to the prefix, i.e. "[TF2 STORE]"
(TF2 being a lame example )