I found a tentative solution that currently works for me in Chrome on Mac OS X. You can check out my answer below for details. For those of you who are sti
I see this as a design having a top a middle and a footer. The middle section contains both the pink and blue columns.
Using CSS, place a repeating image in the background of the middle-section behind both the left and right columns. This image would show the edges of both columns. Hopefully your design will accommodate this. I admit I do not know, without really digging into the code, how to make the middle expand all the way down to the bottom. I should think there are some different ways to approach this.
Use css overflow: auto; for your pink column; for the blue, set overflow: auto; on the or tag.
I hope this helps...