Which of the following colors is considered achromatic?

Achromatic colors are those that lack hue and are typically associated with shades of gray or are completely colorless. In this context, black is considered an achromatic color because it represents the absence of light and therefore does not have a specific hue like the other options listed.

Blue, red, and green are all chromatic colors; they can be identified based on their specific wavelengths of light and are associated with distinct hues. In contrast, black is simply the darkest shade, contributing to the category of achromatic colors along with whites and grays. Understanding the concept of chromatic versus achromatic colors helps in color theory discussions and applications in various fields, including floriculture.