A first iteration at estimating beer color involved simply calculating the Malt Color Units (MCUs) of a recipe.
* MCU = (Weight of grain in lbs) * (Color of grain in degrees lovibond) / (volume in gallons)
For multiple grain additions, you can simply calculate the MCU for each addition and add them together. MCU provides a good estimate of SRM color for light beers, but starts to diverge as beer color exceeds 6-8 SRM, because light absorbance is logarithmic and not linear. For a more accurate estimate that holds for darker beers up to about 50 SRM, we turn to the Morey equation:
* SRM color = 1.4922 * (MCU ** 0.6859)
The Morey equation provides an excellent estimate of beer color throughout the range from 1-50 SRM, and is the one used by most brewers today.