The 'diamonds' related to the diagramming test are a sort of secondary action which is applied and restructures the order of the sequence after you've performed the primary actions such as reverse colours etc.
So for example, in the hardest questions of the test towards the end, there are 4 boxes to perform actions on and then at the bottom of the chain is a diamond attached indicating that a restructuring/reordering is required like reversing the whole sequence, in reversing it means reversing the order after the result of the commands, so 1-2-3-4 becomes 4-3-2-1 etc.
Hope this makes sense, the diamond attached questions come about half way through the test if I remember correctly. Make good use of the scrap paper and you should be ok. Good luck.