Hi Bubbles, I see what at first I thought was air bubbles in the tubing too. The 1st time I saw them I marked one with a piece of tape, and let it go over night. In the morning I looked, and I used 3 - 4 units basel, and a couple more for breakfast, but the bubble didn't move as I was expecting. This yesterday after reading this, and knowing I needed to change sites, I cut the old tubing where I saw the bubble and pushed what was left in the reservoir thru, and I saw insulin right away. So now I think maybe discoloration, and am worried about something else... is it a chemical reaction between the plastic in the tubing and the insulin, that might be putting unwanted stuff in our bodies, or maybe just something sticking to the tubing (no reaction). The later seems to be supported by my pump educator, she was telling me why important to change sites e3very 3 days because insulin would stick to the tube, and would not deliver the right amount. I don't find a big difference in my BG levels when I notice them, so I just change my site, and tubing when scheduled.