Layer slices on groups
Creating a layer slice on a group isn't possible in Photoshop. However converting the group into a smart object lets you add a layer based slice. Select the recently converted smart object and choose Layer > New Layer Based Slice.
Managing colour assets
Updating multiple instances of the same colour in Photoshop is so frustrating. Eleviate this pain by storing your colours in smart objects and using vector masks. For every copy of your smart object you have updating it once will update all your assets with the same colour. Sweet!