Hi George.
It was certainly not unusual for soldiers to request clothing from home. I can cite numerous letters requesting clothing, even though the parent units were well supplied. Part of this can be put down to the soldier's personal taste in clothing, wishing to make himself stand out from others, or more likely, to have spare clothing on hand.(You can never have too much clothing).
Judging from the letter that you provide what is happening can easily be explained. During this period of the War the 'Commutation System' was implemented to ease the burden on the overstretched clothing depots. The individual soldier/company/regiment provided their own clothes and were recompensed by the Government. Many companies and regiments issued orders to the men to provide their own uniforms, providing details of the type of cloth, color and pattern which had to be adhered to. (I did notice that a distinct color and button number were specified by Richard in the letter). When all the uniforms reached the troops the QM would report the unit as being uniformed. Black uniforms were not unheard of this early in the War.
Very interesting piece of family history there.
Jeff