Tab Gamemode is a lightweight and useful Minecraft mod that adds a gamemode indicator for every player directly to the player list (Tab menu).
Instant Visualization: A compact text tag representing the player's current mode is displayed right next to their ping.
Color Coding
[S] - Survival (Green)
[C] - Creative (Gold)
[A] - Adventure (Gray)
[Sp] - Spectator (Aqua)