de hueso colorado
 

I know that at least in Mexico they use the phrase de hueso colorado. For example:

Es católico de hueso colorado.
He's a die hard Catholic.

Is this idiom used in other areas as well?

Never heard it.

Thanks, it must be a Mexican saying.

I, like Gemma, never heard of it. But it sounds really suggestive. I like this word very much: colorado.

I'm trying to guess a possible meaning or explanation for this saying. It could be something like:

• Es católico a hueso colorado: hasta que se le ponen los huesos colorados, es decir, siempre.

También se dice, hasta la médula.