Stars appear to have different colors due to their surface temperatures and compositions. The color of a star is primarily determined by its temperature, which is linked to its spectral class. The most common spectral classification system is the Morgan-Keenan (MK) system, which categorizes stars from hottest to coolest as O, B, A, F, G, K, and M, in order of decreasing temperature.

1. Temperature and Color: Stars emit a continuous spectrum of light, but as the temperature changes, the peak of this spectrum shifts. Hotter stars emit more blue and ultraviolet light, while cooler stars emit more red and infrared light. Here's how the temperature-color relationship generally works:

- Blue Stars (Hot): Stars with temperatures above 10,000 K appear blue or blue-white. These stars are among the hottest, and their light is dominated by shorter wavelengths.

- White Stars: Stars with temperatures around 7,500 K to 10,000 K appear white. They emit a balanced spectrum of colors.

- Yellow Stars: Stars with temperatures around 5,000 K to 6,000 K appear yellow or yellow-white. Our Sun is a G-type star and falls in this range.

- Orange to Red Stars (Cool): Stars with temperatures below 5,000 K appear orange, red, or even deep red. Cooler stars emit more long wavelengths, which are perceived as red.

2. Composition and Spectral Lines: The composition of a star's outer layers can also influence its color. Different elements and compounds absorb specific wavelengths of light, causing dark lines or bands in the star's spectrum. These absorption lines can affect the overall color that we perceive. For instance, if a star has a lot of certain elements in its atmosphere that absorb blue light, it might appear more red or orange.

3. Atmospheric Effects: The Earth's atmosphere can also influence the apparent color of stars. When light from a star passes through the atmosphere, it can be scattered and refracted. This can cause stars to twinkle and can also slightly shift their perceived colors, especially when they are near the horizon.

4. Binary or Multiple Star Systems: In some cases, stars might appear to have different colors because they are part of a binary or multiple star system. The combination of light from two or more stars with different temperatures and colors can create a visually distinct color.

It's important to note that the color of a star is a combination of these factors, and the human eye might not always perceive the subtle differences accurately. Additionally, a star's color can change over its lifetime as its temperature and composition evolve.