Here's just a quick post. I actually made this cake months ago and forgot to post it! You've probably seen lots of cakes decorated with M&Ms online as it seems to be a trend. I thought it would be a fun, casual way to decorate a cake and didn't want to be too fussy with my design. As you can see, my pattern is a little random. You could definitely be more exact with your design - making the side stripes line up with the top or make them go around the outside horizontally or create more obvious circle or flower patterns, etc.
FYI - all those M&Ms make it a little more difficult to stick the candles in a birthday cake!