How to trap invalid enum input exception?

Hi all, I have the following defined in my database:

CREATE TYPE side AS ENUM ('right', 'left');

And I've defined a function that with a parameter of this type.

CREATE OR REPLACE FUNCTION test_input ( p_side side ) ...

Now I test the function with an invalid value:

db=# select test_input('blue');
ERROR:  invalid input value for enum side: "blue"

I want to trap the exception in my function
EXCEPTION
    WHEN ??? THEN
        RAISE EXCEPTION ...

I tried the obvious INVALID_INPUT_VALUE with no success.

Two questions:

1) What is the actual name of the condition (and, yes, I looked through appendix A trying to figure it out) for invalid
enuminput? 

2) Is there a way to retrieve the error code so that I don't have to guess at the condition name?  (I've been playing
thisgame a lot with other exceptions and I don't understand WHY the condition or code isn't provided when an untrapped
erroroccurs)  Clearly, I'm missing something! 

As always, help or informative redirects muchly appreciated!

- Leon