Today's color schemes tend toward the coordination of colors and tones. But colors don't have to be an exact match from one item to another. Adding lighter and darker tones or values of the same color can add depth and a personal feel to a room rather than everything being "matchy-matchy."
Wood and Colors
No, woods typically don't have to match if it is furniture and flooring. In the kitchen, however, wood cabinets should share tone with a wood floor in the same space.
But combined with light colors, they might. It's high-contrast colors that make a room feel smaller. The less contrast in a space, the larger it feels, whether the colors are all light or all dark.
You can create a successful color palette for a space with anywhere from one to five colors. But limiting the number of colors doesn't mean you have to limit the range of values (tints or shades) of each of those colors within a room. You could use even more colors, but you need to be aware that the more colors used within a space, the busier it can feel, which in turn can make it feel smaller.
There is certainly nothing wrong with ridding yourself of unnecessary items every now and then. Using a particular color can minimize the impact of items within a space, however. It comes down to contrast: the difference in colors and values between the items and the walls behind them. The less contrast you have between unsightly objects and the wall behind them, the less easily they will be seen by the eye. The less contrast of colors within a space in general, the larger it feels and therefore the less cluttered it feels. And you can keep this theme going by directing attention away from less desirable objects by creating a strong color contrast in other parts of the room.
All colors go together if you put them together. It's a matter of taste and trend when looking at color combinations. Some color combinations are unpopular because they remind us of a time gone by, while others seem fresh and new. It's simply based on our experience and our tastes at the time. When a color combo is hot, items in that combination are available everywhere, making it easy to include in your decor. Less popular combinations are harder to find, so they happen less frequently and perpetuate the idea that they are unpopular or "out."
An accent color is a color that stands apart from any of the other colors within a room. Accent colors appear less frequently in a color scheme but, as a result, often have the greatest effect. Used wisely, they are excellent for highlighting architecture and furnishings within a space.
The Color Black
Black, or more recently, dark brown has been added to spaces to help balance a color scheme. Like white, black has a neutralizing effect and offers a break to the eyes as it surveys all the colors of a space. It can also add depth and dimension to any room. Likely you have black in your room if you own any electronics, wrought iron or stainless steel appliances, so you may not need to add more if any one of these is present.