How to type “:” (“colon”) in regexp?

In most regex implementations (including Java’s), : has no special meaning, neither inside nor outside a character class.

Your problem is most likely due to the fact the - acts as a range operator in your class:

[A-Za-z0-9.,-:]*

where ,-: matches all ascii characters between ',' and ':'. Note that it still matches the literal ':' however!

Try this instead:

[A-Za-z0-9.,:-]*

By placing - at the start or the end of the class, it matches the literal "-". As mentioned in the comments by Keoki Zee, you can also escape the - inside the class, but most people simply add it at the end.

A demo:

public class Test {
    public static void main(String[] args) {
        System.out.println("8:".matches("[,-:]+"));      // true: '8' is in the range ','..':'
        System.out.println("8:".matches("[,:-]+"));      // false: '8' does not match ',' or ':' or '-'
        System.out.println(",,-,:,:".matches("[,:-]+")); // true: all chars match ',' or ':' or '-'
    }
}