As long as they don't wear their kilt back to front I have no problem with how anyone else wears the kilt.

The importance of knowing the 'rules' is that there is little in life more embarassing than breaking a 'rule' by mistake.

I also think that avoiding a clash between patterns and/or colours helps you to look like you chose what you are wearing instead of just threw something on. IMO tartan sweater and tartan kilt is OK and they shouldn't match but the colours shouldn't clash violently either. Tye-dye shirt and tartan kilt is not OK, but with a solid colour kilt it would be fine. Just like the old 'rule' that only one of a tie and shirt should be patterned and the other plain.

I have never followed tradition, and I'm not likely to start now at my age, but that doesn't mean that I want to look like I am dressed in a clashing combination of clothes because I didn't pay any attention to what I put on.

Black tie and formal attire generally are a special case, but the key is to dress in a way that shows you understood what was asked and aren't so penurious that you couldn't afford to comply (even if you are).