From Star Trek: Theurgy Wiki
Based on the conditions and circumstances existing at any given moment, a starship would assume one of several operating modes which dictate which systems become (or remain) active, the preparations made by the ship’s personnel, and so forth.
The following brief descriptions indicate what each mode involves.
The standard operating mode during non-crisis situations. Level 4 diagnostics were run on all primary and tactical systems at each shift change. One major power system operational; at least one maintained at standby. Long-range sensors and main deflector was in use if ship was moving. A minimum of 40% of phaser bank elements and one torpedo launcher were on cold standby status (available for full activation in two minutes). One shuttlebay was maintained at five minutes launch readiness.
This mode indicated that the ship is prepared for a potential crisis situation. Level 4 diagnostics run on all primary and tactical systems. Power and propulsion systems brought to full operating condition. At least one auxiliary power source brought to hot standby. Phasers, torpedo launchers, and battle bridge (if any) brought to partial standby.
This mode indicated an actual state of emergency; it’s established in, for example, any combat situation. Level 4 diagnostics were run on all primary and tactical systems every five minutes. All sensors were brought to fully operational status. Shields were brought to tactical configuration and weapons and battle bridge to full standby. All shuttlebays and potential fighter bays were brought to 30 seconds’ launch readiness. Isolation doors and force fields were automatically activated as a proactive measure to contain any potential damage.
Ships with planetfall capability had to declare a Blue Alert before starting the descent. This alerted all crewmembers to assume their Blue condition stations and prepare for the landing. Level 4 diagnostics were run on all primary and tactical systems. Power and propulsion systems were brought to full operating condition. At least one auxiliary power source was brought to hot standby.
This mode was designed for maximum power conservation in the event of fuel shortages, failure in the power generation systems, or tactical situations which require that most power be diverted to tactical systems. The crew performed a cold shutdown of the warp engine unless the ship’s traveling at warp speeds or it was the only remaining source of Power (or soon likely to be). Hourly energy budgets and consumption reports were made to the appropriate persons. Weapon systems were brought to cold shutdown unless deemed necessary. Some systems (IDF, SIF, main deflector, environmental systems) were operated at minimum levels; others (transporters, replicators) mightn't be used without special permission.
Invoked for “stealth” missions, Grey Mode was designed to minimize a ship’s profile to enemy sensors. All active sensor sweeps and communications outside the ship were forbidden. All non-essential systems, such as lighting, replicators, and holodecks, ran at half power or might be used only with permission (as appropriate). Any shipboard activity which might alert an enemy to the ship’s presence was curtailed.Grey Mode gave the ship a reduced power signature.
On ships which had saucer separation or multivector attack capability, this mode applied while the vessel was separated. For the most part it resembled Cruise Mode, unless other Alert conditions apply. The IDF and SIF of the two “parts” of the vessel are usually set to high output.
This mode applied when a ship was docked at a starbase or similar support facility. It signified a state of reduced activity, where many ship systems were completely powered down and many personnel were on shore leave.
Some of the texts are edits from LUG sources.