dyed-in-the-wool

Permanent and or firmly established, such as in one's opinions or beliefs. Good luck getting him to listen to your political views—he's a dyed-in-the-wool liberal. Grandma is a dyed-in-the-wool Catholic and has probably never questioned the church once in her life. Uncle Ned is a dyed-in-the-wool conservative, so you'll probably hear him heaping praise on Ronald Reagan before the night is over.

dyed in the wool

(of a person) completely and permanently fixed in a particular belief or opinion; inveterate.

If yarn is dyed in the raw state, it produces a more even and permanent colour.

dyed in the wool

Thoroughgoing, complete. The term, which dates from at least the sixteenth century, alludes to cloth made from wool that was dyed while raw (before it was spun) instead of being dyed piece by piece. The color therefore was “true” throughout, and this concept was transferred to other kinds of genuineness. “In half an hour he can come out an original democrat, dyed in the wool,” said Daniel Webster in a speech (Feb. 10, 1830). It has been a cliché since the early 1900s.