Ironically enough, that's a platform choice: it's the tractor emoji glyph, U+1F69C. On lots of platforms it's red or yellow :-) (Not on desktop Firefox, which is where my screenshot came from in the blog post.) Switching to dark mode may help it be a little more visible for people who find it a problem? It's a good point, though...
That's a fair point. I tend to think in prose rather than visually, so I don't have diagrams already, but it would have been a good idea to put together graphical things to go along with the post to make it a better explanation! Good suggestion. Are there drawings or diagrams that you think would have been particularly useful?