From what you describe, you have a color head for a Bessler enlarger. I am unsure if it will fit your enlarger without seeing it. It would normally replace the condensor lamp house. It is not used in conjunction with the condensors but rather instead of the condensors. The effect will be beneficial to the excessive contrast that you mention with your older negs because it is a diffuse light source.
The color head can be used to duplicate contrast printing filters for use with variable contrast paper. I would imagine that you have Cyan, Magenta, Yellow fitration. Cyan would have the effect of lowering contrast and Magenta would increase contrast.