This is a bit odd with my congis too when I saw yours and made me think....
My oddball patterned congi have also a dark base color while the one with the regular patterned are more yellowish or we called them blond in color. Lol! Same with Fishncash congi. He's also with a regular patterns and also a blond. Same with CDM's. Not sure why but may need to see more pics of other people's congi with regular pattern and oddball patterns.