Each place we visit in most cases both physical and digital have a pattern or flow around them. Lingo is used or clothing types are worn that form the figurative edges of that section. If you've ever walked in a room and it went quiet while everyone turned to look at you than you obviously broke their pattern. Its the analysis and understanding of that pattern that allows you to blend into your selected area. The persona you choose can either grant you the keys to castle or have you locked out forever.
The cardinal rule is to mix yourself into the image that fits into the majority of the group you want to fit in. If you want to blend in at a Scottish festival you better not skip leg day. At the same time if you wear that to most social events of a formal nature you won't blend in. I see a lot of posts in various groups about how wearing a pair of camouflage pants or shoes immediately marks you as a beacon of armed freedom distribution. If you simply apply the majority rule you realize that such things are less important than where you wear them.
"The majority rule is that you look, speak, or act like more than half of what the target population you want to blend into does."
To demonstrate this lets examine an area one would perhaps want to blend in with.
First off if your information gathering consists solely of a google search you're only setting yourself up for failure. Look into what the groups baselines are from the outside without getting close enough to burn your next attempts. What we can see from the above is that multicultural and gender are prevalent. Along with that you have a wide range of people wearing anything from a simple shirt to collared button ups. The age range is pretty varied as well but the majority are pretty clean cut. What you don't see is anyone looking like this:
If we edited this guy into the first picture you would likely spot him pretty quickly. The intent is to follow the majority rule while not disrupting the herd so to speak. There is no dark art to disappearing but instead its simple research and deduction. Like most of the things ranted about on the internet if you sit down and examine the goal you can find the simple solution.
The Majority Rule.