We don't have an output for actual shadow mattes yet. I know there are some situations where you really need a shadow matte, but in most cases there are other ways to do this. Shadows are just the absence of direct light, where only indirect light remains. So if you adjust the Surface Indirect element (tgSurfIndirect), you can adjust the shadows.
To do this, you can subtract tgSurfIndirect from the beauty element, colour correct tgSurfIndirect, then add it back in.
It does slightly affect the sunlit parts too because they are the total of both direct and indirect light, but has the most noticeable effect in the shadows. You can also use the same trick to adjust the non-shadowed parts, by working on the tgSurfDirect element instead.
Matt