I gratified our wooden building blocks.
I bought a couple of permanent pens, an opaque white one, a black, a fine gold and silver. The metallic and opaque pens are expensive however i new that i would use them on other projects so that's ok. 2 pens would be more than enough to alter the look of your blocks and inject some style or even make them educational.
You can write letters, or sound combinations on them and use them as a learning tool. You can draw animals, people, aliens, cars whatever characters you want so your kids can role play a story. And you can just do patterns to make building towers more fun.
Older kids may want to join in too. Have fun go wild and graffiti your blocks too.
Sorry about the picture quality these were taken on my phone.