What does green stool for 2 days mean in adults?

Not much: This is usually diet related. Colors to care about: black like tar, red, maroon, and totally white.

By itself, not much: The color of stool varies with foods, speed of emptying of the GI tract, medications & supplements ingested, gut flora (unique for each individual), additives (like blood), subtractions (like absent bile), infection, inflammation, & other factors. Consider what you ate in the last few days, but if greenish color is unusual for you & persists or is accompanied by other symptoms, see your doctor.