Photo - sepia toned squares
Coins - pewter shades including some green and red (copper and iron oxitdation) you can see the shapes by looking at the shadow areas for what shape something is.
Twigs - various shades of brown, some are red and some are green (these seem to be the easiest to spot)
Bugs- as out of all five games I have going I have only found one bug, a red butterfly.