Have you looked at a field recently? Spot the flowers: https://wallpapercave.com/field-of-flowers-wallpaper - I'm not sure what you call colourful; but I call those colourful. The flowers are still hard to miss. The colour makes them more obvious.

If you want a more academic source; try https://www.stat.auckland.ac.nz/~ihaka/courses/120/Lectures/... slides 13 & 14. Colour isn't some random distraction, the human vision system uses it to help decide what to focus on. Then you get things like peacocks where they go all in on using colourful visualisations to attract attention.