Edit text and style USPS shipping module?

A recent customer reported he could not "continue to the next step in the ordering process". His screen-shot showed an error in his zip code, but the message from the USPS shipping module was small and not noticeable. The customer didn't notice the message and assumed a site error.

Does anyone know a way I can edit the string of the message displayed when a 'bad' zip code is entered by the user...and maybe possibly style it to be a different color only when there is an error?

baldwinpines.com
v1.5.0

Thanks so much.

In your admin use the developers tool kit and search the files for the specific text
When you have determined what file it is in you should be able to change it

Thanks so much for your reply.

I tried adding my string into each of the boxes (one at a time) on the tool kit page and the search kept coming up empty.
Is there anything else you might suggest I try?

Thank you again!