It's this suit jacket from express. unfortunately I can only find this very small picture. But a medium gray tone with a windowpane design. It's a polyester/wool blend, so it's pretty light and has a slim fit.
I'm kind of just wondering what color shirts would be good underneath it. My main focus is on t-shirts, but I'm not opposed to button downs. I'm just afraid that a button down with the blazer might look too formal for the "I don't care" look I'm going for.
But yeah mostly I just need help with colors, because for some reason I'm at a loss with this shade of gray.