I think that's good advice—great, even—for the person just learning to code. Its terrible advice for someone who is or wants to be a professional in a field in which continuous self-education is an imperative to stay employed. Patterns provide both a vocabulary and a toolbox to go to when you're solving a problem. If you don't learn the vocabulary and the tools that are available, you don't recognize problems when they arise, or you only recognize them because you're no longer able to constructively execute on new features.

To take your example, yellow-on-yellow isn't an aesthetic assessment, its a functional one. You recognize that functional anti-pattern because you've experienced, at some point in your life, what happens with a lack of contrast. If you aren't colorblind, you probably don't (intuitively) recognize that red on green is also a functional anti-pattern. When you extrapolate to the world of software development, without having previously learned these patterns or something resembling them, you don't recognize the antipatterns when they occur.

I'm not saying "Don't write software until you know all the patterns, ever." I'm saying that DHH has a traditional antipathy for any pattern he hasn't deigned fit to include in Rails canon, and that when you're coding solutions that need to scale in both performance and complexity, you probably don't want to take advice from someone who thinks a formalization of the AR pattern is the height of domain modeling.