Which root word is associated with the color red?

The root word that signifies the color red is "erythr/o." This root comes from the Greek word "erythros," meaning red, and is commonly used in medical terminology to describe red blood cells or conditions associated with the color red.

For instance, in terms like "erythrocyte," which refers to red blood cells, the "erythr/o" prefix helps to indicate the red coloration of these cells. This root is widely recognized in various medical contexts, particularly those related to blood and circulatory health.

Other options relate to different concepts: "poikil/o" refers to irregularity, "splen/o" relates to the spleen, and "thromb/o" is associated with clotting. Therefore, they do not pertain to the color red, which reinforces why "erythr/o" is the correct choice.