There is an issue with testing for dropped items with a damage value that seems to have reappeared after being fixed in the past. I entered '/testfor @e[type=Item] {Item:{id:minecraft:sand,Damage:1s,Count:1}}' next to some dropped red sand and it gave the error message 'item.tile.sand.red did not match the required data structure'. This should have found the item.

Update: This seems to work in command blocks but still outputs an error message if typed in the chat bar.