The British officer corps was a world unto itself within the British army.  Officers were typically gentlemen who had means and usually some education, whereas the rankers usually came from the lower strata of society: underemployed agricultural hands, skilled and unskilled laborers chief among them.  Officers purchased their highly expensive commissions, rather than training in a military academy or by rising up through the ranks.  Typically, a young gentleman would purchase--or have a purchase made for him--his ensigncy, the lowest commissioned officer rank, for the princely sum of £400.  Higher ranks could be purchased at greater prices when an availability appeared.  Often times a retiring officer would sell his commission, usually at an inflated rate, to another looking for promotion, and use the proceeds as a fund for his retirement if needed.

Subalterns (ensigns and lieutenants) gained their military training by being drilled in the ranks by the serjeants initially, and once proficient in basic maneuvers and the Manual of Arms, learned on the spot.  At the time, many booklets and instruction manuals were available to officers interested in learning the finer points of war and military conduct, but there was nothing as regulated and formalized as found today.

The high cost of commissions meant that in peacetime, an officer, if he did not have the means, could stay a subaltern for years and years until an availability appeared.  During wartime, however, an officer could have reasonable expectations for promotion without purchase, in the event of a superior becoming a casualty.  The vacancy would be filled by the next junior officer and all those under him would enjoy a promotion in turn.  It was not uncommon for Georgian officers to toast "a bloody and pestilent war" that they might gain higher rank without purchase.

Uniform -

The Royal Warrant of 1768 specifies that the officers uniforms should be the same cut and style as the men, although the officers themselves had to purchase their own tailored uniforms and typically used high quality wool of a brighter shade of red.  The 35th's officers wore silver lace around their buttonholes and all other appointments were to be silver--their hats, gorgets, and swords.  They wore neckstocks of black velvet instead of linen or horsehair.  Grenadier officers had bearskin hats like the men but could wear a cocked hat if they so chose.  Grenadier officers, unlike battalion officers, wore a silver epaulet on both shoulders, rather than one on the right.  Grenadier officers were also distinguished from the battalion by carrying fusils--smaller muskets--rather than spontoons, which were long pikes.  Around their waists, all officers wore a crimson sash.

It is speculated that officers wore their sashes and gorgets to indicate they were on-duty and took these off when they were off-duty.  A considerable amount of lieniency was afforded to officers in the matter of their uniforms.  Many chose to wear boots instead of gaiters, especially if they had a mount, and it would not be too uncommon--though frowned upon--for officers to appear wearing some of their civilian clothes.

The 35th Regiment's Grenadier Company had four known captains during its service in the American Revolution.  

Capt. James Lyon, start of war - June 29, 1775 (dead of wounds, Bunker Hill);
Capt. Charles Stuart, June 30 - Oct 7, 1775;
Capt. Erasmus John Phillips, Oct. 8, 1775 - January 2, 1777 (murdered);
Capt. Hugh Massey, March 6, 1777 - end of war.