They’ve newly painted zebra crosswalks in parts of Somerville. When it’s sunny and you bike over them, they are a glaring white so bright as to confound.
And in front of you a circular rainbow pops into existence on the ground; it glides along right ahead of you. It looks a bit less than ten feet in diameter. It’s on the pavement as well as the white stripes, and slowly fades after you’ve moved entirely past the crosswalk.
This worried me until this morning. Why would I see the rainbow when I’m not even seeing the crosswalk anymore? Fun door-opening and fun cognitive science have opened my eyes to some weird quirks of perception (hey kids! what color is dry new snow on a sunny day?), but this one was new to me, and I had to assume it to be a harbinger of brain damage.
But this morning, biking at a more leisurely pace and willing to look away from the road for a while for science, I figured it all out. The painting process had left a near-invisible coating of dust on the road all around, and it was this that was reflecting up the rainbow. My guess is that they make the road paint on the fly by mixing some goopy junk and some really fine smashed-up crystal powder of some sort, and they didn’t have enough goopy stuff in the mix this time.