Yes, sativas due tend to be lighter than indicas. Pure indicas are very dark green, and pure sativas are very light green. It would be impossible to pin point what strain or genetic it is just by looking at dried buds. Even when the plant is growing, an unknown strain will remain unknown. There are just so many kinds of buds out there. Since someone realized how easy it is to cross strains in their own homes, the results are endless.

But yes, the darker it is, more indica, more lighter, sativa, and if it's a happy medium, then it's a cross. Which most strains are crosses these days as finding a pure sativa is a difficult task.