Planetary nebulae come in a variety of colors, but some of the most common include:

* Blue: Caused by the emission of oxygen.

* Green: Caused by the emission of hydrogen and oxygen.

* Red: Caused by the emission of hydrogen.

* Purple: Caused by a combination of blue and red emissions.

However, the exact color of a planetary nebula depends on the specific elements present and the temperature of the central white dwarf star. Some nebulae may even appear to have multiple colors within a single object.

Here are some examples:

* The Ring Nebula: A classic example of a green planetary nebula.

* The Helix Nebula: Shows a blue and red color variation, making it appear purple.

* The Cat's Eye Nebula: Exhibits intricate patterns of blue, green, and red.

Ultimately, the colors of planetary nebulae are a beautiful testament to the diverse chemistry and physics at play in these fascinating celestial objects.