You refer to the bulb as being an 85 Watt halogen bulb. I think you may mean an 85 Volt halogen bulb, because my Beseler colour head (for a different enlarger - a Beseler 67 series) happens to use a halogen bulb with that rating.

Over the years, Beseler has made a number of different colour heads that have different power supply and bulb requirements. You may have something that is mismatched, or there may be a problem with the power supply for the head, or the dichroic filters may be sticking - there are a few possibilities.

In my case, my enlarger often produces too bright a light - my exposure times can be inconveniently short.

Do you have pix of the head and the power supply, or at least model numbers?

Matt