Variables are not highlighted

[bnSonic]

I'm not a RegEx-Expert so i don't really understand, how the SQL-String should look like, to have variables in a different color.

For example:
string sql = "Select field1, field2 From table1 Where field1 = 'string' or field2 = :parameter";

neither 'string' nor ':parameter' is highlighted.
Is this a bug or do i misunderstand the term "Variables"?