Hi Andrew, how long have you had this? Have you recently travelled outside the country?
Thanks for the picture. Can you describe the area that you are concerned about? Your ear looks to be within normal limits overall, and I don't see any obvious signs of trauma, bug bite, infection, etc. It can be a bit tricky, however, as the ear is a very vascular structure and its colors can vary from one part to another depending on how dilated or constricted the blood vessels are in each region. This, in turn, can be influenced by external factors such as ambient temperature, or internal factors such as one's emotional state. If you had a dilated vein present before, it may have constricted or flattened to the point where you can no longer see it.
Yes, sunburn could certainly do this...and a couple more days may make all the difference. :-)