Hopefully you are seeing plenty of pollen entering the hives. The menu page "Bee Friendly Plants" with it's sub-menu "Pollen colours" might help identify the source of the pollen. However, the big problem is that it isn't in colour! If any one can point me in the direction of a good colour chart then let me know and I'll get it posted. I've made a start with this link which is also on the above menu page.