Why do the upper levels of Neptune's atmosphere appear blue?

The upper levels of Neptune's atmosphere appear blue because of the presence of Methane in its atmosphere.

Explanation:

Neptune -

Neptune is the eighth planet of the solar system,

The composition of Neptune's atmosphere is mainly hydrogen, helium and methane gas.

The Methane in the atmosphere of the Neptune absorbs the red light from the sun and reflects the blue color into the atmosphere, Hence,

The atmosphere of Neptune appears to be blue in color.