i took notice of when the birds begin sent they used to have rosey pink flesh, however on return from the race the flesh would appear to be blueish. I have read blue flesh is a sign of build up of toxins, and is also visable when feeding protein as the toxins supposably build up. I found out the way of removing the toxins was in the above method, which i found out from best of british video. It worked for me as on return from race blue skin, but on the evening time they returned back to rosey pink. Whether right or wrong, this was the process i used to do, i do not have any scientifical knowledge to answer your question of the build up of toxins, just my observations and readings!