Hair color

Why was the hair color of the two actors (who played Paul and Chouquet) so obviously (and badly) manipulated? Neither of the two were sporting their real hair color, and I'm wondering if this was done deliberately to further distinguish between the three roommates---although I've no idea why that would have been necessary. Normally I wouldn't have minded so much, but in a film with so few major players, to have them stand out this way was distracting.