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How do planetary nebulae differ from one another?

Answer 1

Planetary nebulae vary in mostly size and color.

A Planetary nebula "is a kind of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from old red giant stars late in their lives." [1]
Planetary nebulae actually have nothing to do with planets. They are called such due to the planetary shape of the nebulae. The name was coined by William Herschel.

Most nebulae are composed of mainly hydrogen which causes most nebulae to appear red in part Balmer series emissions.
If more energy is available other elements, like helium and oxygen, will be ionized causing a green and / or blue color.

Further Reading:

Planetary Nebulae

A video of nebulae sculpting

Emission Nebulae

Various Nebulae -

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Answer 2

Evan Ashley

The main differences between planetary nebulae are their size, shape, color, and composition, which are determined by the parent star's mass and age as well as the conditions in the interstellar medium where they form.

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