Color theory is what most fashion designers and experts use to mix, match, and manipulate colors. You can use color theory to create entire outfits with combinations of warm and cool colors, all working together to achieve a particular style.
It's important to say that you should consider not only primary colors but the colors that sit next to them, also known as analogs. These are colors that complement each other and look great together, even though it might not seem like it, like blue and yellow for example. However, it is not recommended to use too many colors in one particular style. Try to stick to 2 to 3 colors between your clothing and all your accessories.
You should also try to ensure that the colors don’t clash. For instance, if you are wearing neutral colors, or all black, adding a blue hair accessory could be the ideal solution. On the other hand, if you are wearing a variety of colors, you could use a neutral or softer color hair accessory to keep the colors from clashing. Mix tones and work within the color groups you've chosen. For example, if you have a royal blue dress, you could try wearing a light blue accessory.