The Uniform

By the time the regiment was raised, the standard for the uniform had already been set by the 1742 Clothing Book. This book effectively removed the influences of the regimental colonel on the uniform and set a certain standard to the quality and presentation of each regiment. Certain regiments maintained individual distinctions and embellishments, however, the 55th/44th Regiment of Foot flaunted no such deviation to the regulations.

Lace and Facings

From its formation probably, at any rate from 1748 until 1768, the regimental tape-lace was white with a yellow centre stripe and black and blue waved lines.
 
After the statute of 1768, where regimental colours and embellishments were laid out in great accuracy, the wavey lines of the 44th were straightened out, and remained so until 1886 when all coloured laces were abolished.

The 44th was an 'unlaced' regiment, so for the officers, a twist of silk edged the buttonholed, red for the jacket colour and yellow to match the facing.

Buttons and Buttonholes

Officers originally wore silver embroidery on the buttonholes. However, this practice was discontinued by the end of the 18th century and their facings were plain, except for a loop of narrow yellow silk twist to the buttons, until 1880.
During the long period (from about 1770 to 1855), when infantry regiments were distinguished by the shape and spacing of the "loops," or bars of lace, across the front of their coats, the 44th wore square-ended loops at equal distances.
The officers had silver buttons placed at equal distances apart, like those of the men. The men of "other ranks" wore pewter buttons. The jacket shown (left) is of a Captain from this period, a single epaulette on the right should denoted rank and the gorget worn by the 'officer of the day'.

left: Officers' silver gilded button from around 1745 (replica)
middle: A brass button from around 1815.
right: Brass button from the latter half of the 19th century.

From 1855 nearly all regimental differences in the infantry, beyond the colour of the facings, were swept away, and even the pewter buttons were replaced with brass ones. Then in 1881, on the amalgamation for the purpose of making double-battalion regiments, all English line regiments were replaced with white facings. The 44th "East Essex" was merged with the 56th "West Essex", the form the "Essex Regiment".
Also, from that year, officers of all regular infantry wore gilt buttons and gold lace loop, which considerably altered the dress of the 44th officers.

Hats and Headware

As with the rest of the uniform, the regiment followed the standard pattern for headgear as well. The early headgear was the black felt tricorn, but towards the end of the 18th century it was replaced with the heavy, stove-pipe, shako, shown on the front page. As regiments returned from home from the campaigns against Napoleonic France, around 1812, the stove-pipe, was replaced with a smarter pattern shako often known as the Belgic shako. This pattern was wore by the 2nd Battalion at Quatre Bra.

left: General issue plate worn on the stovepipe shako during the Peninsular campaign.
middle: Plate worn at Waterloo, 1815.
right: Later shako plate from the latter half of the 19th century.

General

The rest of the uniform followed the standard patterns for the British army of the times. Starting with ubiquitous red jacket and white trousers with black shoes and white knee-high gaiters. Whilst the jacket stayed the familiar red, it's style changed, following that of contemporary fashion. Long tails became shorter and the lapels disappeared altogether. Trousers stayed white up until about 1812 to 1815 between the regiment returning home from the Peninsular campaign and being redeployed for the final battle at Waterloo. In the latter half of the 18th century, the gaiters became black and only reached up to the knee.

Distinctions within the regiment

Each regiment was constructed of ten companies. The 8 centre companies were comprised of regular line soldiers, or battalion men. There were then two flank companies: the light company and the grenadier company. Both companies wore distinctions. Primarily wings on the shoulders (I believe that there is actually a set number of rows of lace on the wings to determine light from Grenadier, but I can't say for sure - please mail me if you know !)
For the headgear, the light infantry wore helmets, until about 1800. when this was replaced with the shako, a green plume was worn. Up until 1768 the Grenadiers wore a mitre, which was then replaced with a bearskin. By the Napoleonic time they were generally reserved for home service dress only, and in the field they wore the same shako as the rest of the regiment, with Grenadier modifications, which generally consisted of having a pure white plume instead of the with over red of the battalion companies.
Drummers, and Fusiliers also wore bearskins.

For the list of references, please see the References section on the Credits page.