Book was from the 1960’s which I purchased at my school’s book fair. About a black and yellow caterpillar who meets other characters along his way. Book cover is green. All characters have large eyes. The caterpillar feels he is ugly but turns into a beautiful butterfly at end of story.
It’s a bit later, but this could be Dream Tree, part of the Serendipity series (words by Stephen Cosgrove, pictures by Robin James).
Some version of the “ugly caterpillar” (ugly duckling) trope–it’s been used various times, such as the book Charlie the Caterpillar. But finding one that would have been sold in schools in the 1960’s–that might be a bit more challenging.
Here’s one to try: Best Foot Forward, by Louise Young. The heroine is Caroline Caterpillar.