de hueso colorado

[Tomisimo]

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?

[María José]

Never heard it.

[Tomisimo]

Thanks, it must be a Mexican saying.

[Alfonso]

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

[Alfonso]

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.