Why don't all electrodes produce the same results in the electrolysis of potassium iodide?
To distill down your observations: you always saw pink at the cathode, but only some materials produced a brown color when used as the anode. This means that the anodic materials that didn't produce brown didn't oxidize the iodide to iodine.  

So, the question is what was happening at the anode when the iodide was not being oxidized. The answer is simply that the anode material itself was easier to oxidize than the iodide in those cases, so the anode itself was oxidized and the iodide was not, so there was no brown color produced.