It looks like an ES socket, but what is the distance from the socket to the centre of the condenser lens? If it matches a standard ES enlarger opal-bulb (which are about 60mm from the top of the brass thread, to the centre of the bulb) I would be surprised, but you never know.
The head does look rather antique so if that is an ES socket-and-bulb then it pre-dates the use of halogen bulbs in colour enlargers. I vaguely recall that halogen became popular due to quantity of light and consistency of the light colour temperature, but there is no need to use the colour-filtration when doing black-and-white printing of course.