Calculating SRM When Caramelizing First Runnings?

I'm going to be doing a SMaSH tomorrow with MO and Challenger and in order to get a bit more color and flavor from the malt, I'll boil down about a gallon of the first runnings in order to caramelize some of the wort. Does anyone have any idea how you would calculate the SRM of the resulting beer? I know it will depend on the amount boiled down and the amount it was boiled down, but are there some general guidelines? I know it's not that important, but I think it would be neat to know.

I doubt that anyone has a way of estimating the color. It's too complex of a problem. I suggest keeping notes on the time and the volume. Maybe you'll have a shot at repeating or adjusting the color.

Kai