I love this photo from GQ.
This guy goes from schlub to well dressed through proper fit, colors, and patterns. The larger check pattern on the after shirt gives a nice contrast which helps frame the face and compliments the guys complexion. In the before photo the guy looks a little pale and washed out because there is not contrast between the shirt and jacket which draws the focus away from the guys face. Choosing the right color combo is like a picture frame for your face. You want it to highlight your features and draw the viewer into the main subject… your face. For this guys complexion he wants to choose colors that have a high contrast. That’s why the large white checked shirt looks so good against the jacket.
Check out that fit as well. He goes from baggy and loose to close and fitted. It makes a huge difference in the way your perceive his body shape. A well fitting blazer will make all guys look good regardless of their size.