A cold light head produces a diffused light, similar to a Color head, but it has a different color spectrum. If your DeVere has a Dichro Color head, I'm not sure you would see much advantage to a Cold Light head, but if your enlarger is a Condenser head, then you will notice a big difference.

Cold light heads originally were a somewhat less expensive diffusion light source than a Dichro color head. For B/W they both serve the same basic purpose, to produce a flat smooth light that minimizes negative dust and flaws on the print.