Colonels typically command regiments of ground troops. This rank is generally the highest rank in any mercenary unit; Even mercenary groups with multiple regiments typically use Colonel for their commanding officer. Occasionally this officer is identified by "Senior Colonel."
To achieve the rank of Colonel in the SLDF, a soldier had to serve for at least ten years. This also showed that the officer had a great deal of tactical skill. The SLDF Navy used the rank of Commodore for this rank. Each rank used a small star as their insignia.
In the DCMS, "colonel" is known as Tai-sa. In 3025, a DCMS tai-sa was a battalion commander and wore an apple green stylized katakana numeral "3" as their rank insignia.  In the Draconis Combine Admirality, the equivalent rank is "Captain."
A rank in the Federated Suns military structure, Colonels usually command regiments. Colonels in the AFFS wear epaulets with two broad bands across the bottom as their symbol of rank. This epaulet is also used by the AFFS' Navy to indicate the rank of Commodore.
AFFS Colonel (Commodore) insignia by branch of service
In 2451 a regiment of the CCAF revolted, killing the Capellan Chancellor's brother. Chancellor Jasmine Liao, as part of her purge of the officer corps, took control of all powers held by divisional and sector level commanders (generals) and prohibited any rank higher than Colonel. For the next six centuries, CCAF Colonels were either Regimental Colonels that commanded regiments or Senior Colonels who were the military directors of a Capellan Commonality. These officers were also responsible for logistics and strategic planning in their Commonality. When Sun-Tzu Liao took the throne in 3052, he created the rank of Sang-shao to replace the rank of Colonel. The CCAF Naval version of this rank became Kong-sang-shao. In both cases, CCAF officers with this rank use a silver triangle to indicate their rank.
In the FWLM a colonel commanded regimental sized troop formations. Provincial rulers were usually given the honorary rank of Colonel. The commanding officers of mercenary units frequently had a rider in their contract that would give them this rank, regardless of formation size.
Colonels in the FWLM used three broad gold bars and one narrow gold bar on a purple background as their rank insignia.
The equivalent ComGuard and Word of Blake Militia rank is Precentor. ComStar Precentors use a ComStar logo with a red halo to show their rank. Word of Blake Precentors use a gold medallion.
Insignia shows theta symbol, indicating JumpShip/WarShip crew. Other service branches replace theta with appropriate Greek letter.
The Magistracy Armed Forces use Colonel to indicate a regimental commander or head of a division within the MAF bureaucracy. Prior to the reforms of the late 31st century, they could also command major Combat Formations, but that role is no longer available. The naval equivalent is Rearad. MAF Colonels wear two small gold diamonds as their rank insignia.
In the Taurian Defense Force, a Colonel serves as a regimental commander for both 'Mech and conventional forces. In the TDF Navy, officers who hold this rank are known as Space Masters. Space Masters captain naval vessels and have command authority over all other aerospace ranks. A TDF Colonel uses the gold circle and horn of the Brigadier as their rank insignia, but fills the center of the ring with a red dot to differentiate themselves from the lower rank.
With their focus on recreating Roman society, the Hegemony Armed Forces do not use the rank of Colonel. Instead officers who command regimental sized formations are known by the Latin term Prefect. Their rank insignia is a gold bordered black triangle with an eagle in the center.
In many of the world's military establishments, a brevet was a warrant giving a commissioned officer a higher rank title as a reward for gallantry or meritorious conduct but without conferring the authority, precedence, or pay of real rank.