Former House Speaker John Boehner is the latest Washington DC luminary with a tell-all book deal — and the cover art alone is worth the purchase price.

These days, book covers are all about nature; they’re festooned with flowers, swirling with birds and littered with leaves. Those aren’t the only trends we’ve noticed, however.

The styling Oprah’s 111th book club pick features type in a shade of yellow that you’ll also see on the cover of the forthcoming “Happiness & Love,” among others. (A similar chartreuse is ...