Everything that will be described here, and every custom it refers to, has solid practical reasons behind it. But it is not a rule.
Some people are fine with having shirts and suits that are similar. Some think they look good in a black shirt and a black suit. I disagree, but that's just my opinion. I would argue that it is always worth knowing why customs exist. If your shirt and suit do not contrast you lose the slimming, broadening effect it can have. Which is fine, if you don't want that. But every custom is there for a reason. Take the time to know why people call them rules.
Hopefully, this blog will help men understand some of the guidelines, rules or customs a little better. They often don't realise why customs exist, and either follow them slavishly or ignore them out of a faint sense of rebellion. It's far more interesting to investigate and then create. It's easier and more fun.
This is my philosophy.