This is my theory: Every time I change the TC oil there is a slight colouring in it, this I assume would be the clutch discs wearing within the TC, so this metal colour is metal circulating through the oil and around TC and into the bearings, so would it be fair to say the TC should be changed often, maybe more then factory specs if you expect your TC to last longer then normal?

 

Something is wearing if you see metal color.

My diff and tcase are clear fluids. Although my trans fluid has metallic color.