dyed in the wool

Short definition from Wiktionary

Verb

1. 1
   simple past and past participle of dye in the wool

Adjective

1. 1
   Alternative spelling of dyed-in-the-wool (Set in one's ways, steadfast.)
2. 2
   Having the fibres dyed before they are formed into cloth.
3. 3
   Firmly established in one's beliefs or habits; having a specified characteristic, identity, etc. deeply ingrained in one's nature.