When the blending mode for a layer is set to "Color", any area it covers with semi transparency has this strange look to it. You can pull the opacity slider of the layer underneath to see the strange interaction as the layer becomes more and more transparent.
Yes, having a solid layer underneath is the workaround I hinted at in an earlier post, but it is nice of you to show how to do it for others who may be encountering the same problem. With Rebelle 6, you can also use the clipping mask on the color layer and not have the visual bug appear.