Why does oil change the color of salmorejo? We did a few experiments last year with salmorejo, a cold soup made of very ripe tomatoes and bread, very similar to gazpacho.

We noticed that while blending, the salmorejo would turn pink. This is because the tomatoes get into contact with oxygen. We don't like the colour/taste of the pink salmorejo. Adding more oil to the soup would miraculously restore the colour/taste.

So, there's the question: why does adding more oil (EVOO) restore the colour of the tomato soup?
When tomatoes are fried, you can see that the oil becomes coloured red - so at least some of the colour components are preferentially soluble in oil.

I will hazard a guess that, under the circumstances mentioned, the oil coats the tomato particles, and some of the colour migrates into it to give a red surface. Because the oil forms a coating, that coat will inhibit oxidation.  The oil will also improve the mouth feel of the soup.

Just the way I see it ...