Richard Scarry and gouache

I've read lots of later Richard Scarry to my son, but we picked up Polite Elephant at the library last week and found it quite endearing. I really was taken with the more rendered style and as I read it (over and over and over) I guessed it might be gouache. After a little searching online - mainly this great post from 7 Important Things Before Breakfast, I discovered ALL his work is gouache! Wow. This, as I just finished an illustration job last night where I just didn't get my cheeks rosy enough and had to boost them in Photoshop a bit. Oh Richard Scarry. I wish I could pick your brain about how you paint such gorgeous, rosy, cheeks.