Sometimes rules are made to be manipulated. In elementary school, I wore a black tennis shoe on one foot with a white sock and a white tennis shoe with a black sock on the other. Funny how I thought I was so cutting edge. However, I am proud that in my youth I thought somewhat out the box.
I love watching What Not to Wear on TLC. At times I find myself amazed at what things people think don't go together. Pink and brown? Yes, you can wear it. Wearing black with brown? It's possible. A print blouse with a non-solid jacket. Tricky, but it can work.
The ruffle striped blouse above I purchased at a thrift store for $3. The ribbon plaid belt I purchased at another for $.99. The colors look like they're in the same family, so why not put them together? The different pattern on the belt actually helps it stand out more. Admit it, you're a little visually intrigued.
Mix and matching is definitely okay. Just try not to look too much like a disheveled elementary school student.