Remember.. the key is NEVER go too overboard. Of course u can get a top that, for example, is purple, white and orange and try to match with that but if you have a multi colored top, go darker (or less noticable) with your jeans. you wouldnt want to look like one huge blob of colors. Try to Choose a piece with some colors and focus on a couple of accessories that go with it. For example, you have a striped blue, green, white, and purple shirt. You can match that with dark jeans and make one of the colors pop out ( for example blue) and add a blue belt of the same color... or even a blue headband. Although i have to say, if you want to look really into fashion, matching perfectly isnt in anymore. Of course it will always look together, but not so much anymore. FOr these seasons trends, you should look into a color wheel and combine complementary colors ( such as orange, red, yellow) and that will look good. Also if you want to make a statement, or be noticed more, You should try opposite colors that pop out and look good to the eye, for example, a black and white dress could easily be matched with white shoes, and a black necklace...but if you match it with red pumps or a red accessory, suddendly the accessory pops out of the dress and you dont end up looking lost in a mutli colored pattern.
I hope this helped and i didnt confuse you. =)
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fashion school ( Art institute for fashion design)