The most common color of the Northern Lights is green.
When it's not dark enough, and Aurora activity is low, then you can see just grey color with the naked eye.
Moon is an additional source of light. Visible moon decreases Aurora visibility.
The fuller the moon gets, the more additional light is produced, which leads to lower Aurora visibility.
This is why the green Northern Lights can be seen as grey when the moon is in the sky.
The Northern Lights can have more colors during the stronger activity. As Aurora gets stronger, the color ranges from grey, green, and sometimes pink.
The visible colors include red, orange, and yellow, or even violet, blue and white during medium to extremely strong Aurora activity.
