Proportion and Color
The best way to describe a proportion is, size. Color affects a rooms visual proportion. A general guide line is white or pale colors make objects recede, while dark or bright colors draw things closer which causes them to appear larger.
In a rental environment walls are generally painted a white or beige color. Most people assume that you are not allowed to paint. If you are planning to stay over a long period of time you may want to ask your landlord if you can paint under the condition you return it to the original color. Most landlords agree to this because it assures them a fresh coat of paint upon your departure. If not you can use other tricks to create your ideal environment.
Whether you decide to paint or just furnish your apartment keep the eye fooling properties of color and proportion under your belt. Lighter recedes, Darker draws in. It works with every style and can be applied to fabric, furniture or accessories!