Is green a soft or dark color?

Colors, also called hues, are generally described by two factors: value and intensity (or saturation). Value is how light or dark a hue is. Intensity is how bright or muted a hue is.

Describing a color as "soft" is somewhat subjective. A "soft green" usually refers to a more muted hue. But for some a lighter value of the hue may seem "soft".

Dark green would refer to adding black or another color that contains black to the original hue.

A muted green could be dark or light.