As Baldrickk notes, it's pretty clearly a rainbow flag as used to signify support for the LGBT+ community, and so was put in the picture by someone who wanted to convey that support rather than it happening to just be a rainbow on the page by chance.
I think it's a nice touch. Others may (validly) not see the point but not have a problem with it, while some others (such as the petitioner) go full-on hate outrage about it (boo hoo). But I don't get those who are saying "it's just a rainbow" - someone has clearly put the flag in the picture to convery a supportive message, in the same way that many businesses or organisations will fly or display the rainbow flag to convey support. Let's not pretend that it's not what it is (and what it is is a good thing).
Anyway, let's hope the petitioner hasn't visited the Pimoroni website: https://shop.pimoroni.com/products/pibow-for-raspberry-pi-3