I'm having trouble finding a link, but there have been user experience studies involving heat maps, etc. showing that any unnecessary visual elements distract t

I'm having trouble finding a link, but there have been user experience studies involving heat maps, etc. showing that any unnecessary visual elements distract the user. I'm with you that I like the idea of having a strong visual indicator to differentiate different posts, but studies in UE have proven that the age-old "use zebra coloring to differentiate rows" that was used in accounting notebooks and perforated printer paper in the mid-20th century up until the 80s draws users' eyes away from the content in order to differentiate. Basically it is annoying to our brains and slows us down, but programmers like straight lines and making things neat, so the aesthetic nature of the differentiation in color and its assumed practical purpose makes us erroneously choose it over the visually simpler option.