Back Inside Cover: Formosan subterranean termites (Coptotermes formosanus). Soldiers have red-coloured heads while workers  have pale-coloured heads. Image courtesy Wikipedia.

Front Inside Cover: Young planetary nebula NGC 6302 (Butterfly nebula) with clear reddish-orange S-shaped gas from ionised iron atoms being blown out at high speeds. Picture credit: NASA/ESA, and J. Kastner

Whole outer wrapper Cover?: Double rainbow in the sky; from https://www.sciencenewsforstudents.org/article/explainer-rainbows-fogbows-and-cousins
. Alexander's band is seen as the dark shadow of unlit sky between the primary and secondary rainbows.
. Figure showing the path of Sun's rays through a raindrop, forming a rainbow. Image credit Wikipedia.