The Color Wheel (as seen above) is the first tool used when designing, creating, etc... Trust me when I tell you some of your favorite designers use this tool when creating looks & world lines. Now the rules of the most basic color wheel are very simple. As seen above there are 3 different letters, the P, the S & the T. P= PRIMARY, S= SECONDARY & T= TERTIARY meaning third.
Shown in the color wheel above, primary colors list as Yellow, Blue and Red. Secondary colors are the colors located mid-point between two primary colors and list as Orange, Green & Violet. Lastly, the tertiary colors are those mid-point between two secondary colors listing as Red-Orange, Yellow-Orange, Yellow-Green, Blue-Green, Blue-Violet & Red-Violet.
This all may seem like a lot right now but these fundamentals are key when decorating or designing ANYTHING. It doesn't matter if it's your room, living room or your outfit for a night on the town, remembering these basic rules will never have you looking like you got lost in a 100 piece Crayola box.