Maybe a volcano erupted in the mean time.
Seriously, dirt color cannot be uniform across the world, and it is derived from the average ground colors and vegetation index value (basically a % covered by vegetation), with lots of voodoo tweaking.
But since the ground color changes as we are getting better data sources, we have to adjust the formulas as well. I think the problem here is that there are new formulas used with old color data. In any case, this is going to change a couple of times yet ...