Planetary nebulae don't have a single "typical" color. While they can be various shades, they're often a beautiful blue-green.

Here's why:

* Oxygen: The blue-green color is often due to the emission of light from highly ionized oxygen atoms. These atoms emit light in a specific wavelength range that our eyes perceive as blue-green.

* Other Elements: Other elements like hydrogen and nitrogen also contribute to the colors, sometimes creating a reddish hue or other variations.

* Age and Composition: The color of a planetary nebula can also change over time as the central star evolves and the nebula's composition changes.

So, while blue-green is common, you'll also find planetary nebulae with red, pink, orange, and even yellow or purple hues!