@Antonio-Guerriero ,
You just want it to be “any token that ends in a : should be considered a LABEL”? Yeah, the User Defined Language lexer isn’t designed to be that complicated: it is intended for a specific list of keywords
The EnhanceAnyLexer plugin will allow you to add a regex to change the foreground of matching text on a per language (per UDL, or per builtin lexer). Assuming that the LABEL has to be the first non-whitespace sequence on a line, and must be only alphanumeric-and-underscore-before-:, then the following should make your LABEL green.
[your_udl_name_here]
0x00CC00 = ^\h*\w+: