aws lex custom slot type with regex fails when using : character

I am trying to create a custom slot that can recognise time format 10:00:00 for example, so i created a custom slot "extended slot type" and tried using regex like this [0-9]{1,2}:[0-9]{1,2}:[0-9]{1,2} it failed with "Check the regular expression and try your request again" error so i tried using the unicode character for "colon" like [0-9]{1,2}\u003A[0-9]{1,2}\u003A[0-9]{1,2} even this fails with the same error i tried using other unicode and special characters like - which works absolutely fine.

so, How can i use a colon special character in regex validation ?