When creating an OC the personality and backstory are the most important aspects. But how will s/he be recognized if her/his hair, face and whole body looks just like an other one's OC?
The answer is simply: her/his clothing! Most people choose their clothing on their own. And not everybody buys the same shirt or shoes.
The choice of clothing is the best way to get recognized because a lot of matters are involved when you choose your new shirt. You consider age, attitude, gender, environment, hobbies, personality and profession (even when you're unemployed).

But let me show you step by step:

Age

This aspect is quite simple:
A baby or toddler will just wear clothes like romper suits and so on. But remember that the one responable for their clothing may also consider the kid's so far shown personality and all the other things I'm going to talk about later.
When the kid gets older, it's a bit different. Parents or people in charge will still be the one buying the kid's clothing but the kid will slowly start to decide on what it wants to wear too. Maybe it will even start to resist wearing special clothing.
This development will go on all their life and as it goes on things like hobbies and attitude will be outweighing more and more.

Environment

What you choose to wear is affected by the people surrounding you (friends, family, even strangers you meet just by chance) and of course the amount of money you can or are willing to spend.
Just imagine a poor family-loving girl in a little village and a rich trendsetter in a big city. There's no way they wear the same kind of clothes!

Attitude & personality

This two aspects make the big difference between e.g. two twinbrothers. They share the same family, (maybe) the same body and face but their personality won't be the same.
Let's say one of them is quiet, reserved and carries a good-willing so-what-attitude. He is most likely wearing baggy and cheap clothes while his company-loving but little mean brother with his we-r-kings-attitude won't ever put down his brand clothes and cap.
Remember that shy people often wear long clothing to hide or tried to fit everbody's style to not stick out.

Let's take me for an example:

I wear practical clothes because I don't care much enough about fitting in and what others think about me.
My clothes are often sporty or college-style because I like doing sports and like the used look because I still want to feel cool (yes, here's my atittude).
I also wear long clothes very often because I'm a bit shy and not really confident when it comes to my own body.
Wearing a necklace became a kind of habbit to me. It shows my unsureness and serves the function of protecting me. Because it's an unussual symbol it also shows who I am and who I want to be.

Just take a closer look at yourself and think of your own reasons and influences or maybe someone you are sure to know well.

Hobbies & profession

Of course there is a difference in how a book-lover and how a sport-loving guy dresses too.
But your hobby isn't that important. It is your profession.
It doesn't matter whether you are a professional artist, an office worker, simply unemployed or a student: You spend most time on your profession.

Just go on and do some research on your OC's profession and hobbies!

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Now to colors!

All these aspects reflect in the colors a person tends to wear too.
The easiest rule would be that shy persons would most likely wear dark or dimmed colors that don't stick out much.
More confident persons usualy wear bright colors e.g. opaqued red or yellow to stick out more.
All in one: The more confident a person is the most likely s/he is to break with the rules.

Again, this is usualy a result of all factors I listed.

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Remember: all of these aspects are connected with each other and do research and research and research. Because the more you do research, the better and more vital your OC will become.