I have never seen this on any of my Ducati's before and it's baffling me. These pictures are taken today after my bike stood for 4 hours sitting at Box Hill, started it from cold and the heat was coming after about 1-2 minutes of idling ,no throttle input. I could understand if i was revving the nuts out of it but i was not? looks like it runs really lean?
I had the same on a 2003 GS1150. Only noticed it when it was dark, but like yours, it seemed to run fine
The headers run very hot.1150s thinner wall lower schedule number. Are your headers equally coloured when cold? They are normally a light brownish colour. Look almost oxidised when cold.
R1100s S version did the same. R1100r not. I’m pretty sure it’s a wall thickness issue. Some 1200s early models did this. If in doubt do a quick plug check for colour. If it runs otherwise OK not generally a concern.