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 '-'
}
}