Perhaps, for the benefit of the non-Mason, I should answer the question "Why do masons wear aprons?" first. Briefly, although there is much debate about where modern Freemasonry comes from, I think it is fair to say that Freemasons wear aprons as a symbolic link to the operative masons who built castles and cathedrals in the middle ages. Early (17th Century) Freemasons wore plain aprons that were made of lamb skin, but these evolved into more elaborate hand painted and decorated examples.
In 1731 the Grand Master, his Deputy and the Grand Wardens (then the only "Grand" Officers) were permitted to line their white leather aprons with blue silk. Masters and Wardens of particular Lodges were allowed to line theirs with white silk and the Grand Stewards for the year with red. When the 'Moderns' and 'Antients' Grand Lodges combined to form the United Grand Lodge of England in 1813, a standard design for aprons was adopted with Master Masons and Installed Masters wearing aprons trimmed with sky blue and Provincial and Grand Officers trimmed with dark blue. Colours and designs of aprons vary in other Masonic constitution (eg Scotland and Ireland).
Grand Stewards are appointed for a year and they are tasked with regulating and arranging the Annual Festival of the Grand Lodge of England and also assist in the arrangement of Grand Lodge Communications. Since 1731 they have been entitled to wear an apron trimmed with crimson and a collar of the same colour during their year of office. In 1723 six Stewards (they were not known as Grand Stewards until 1792) were appointed and the number rose to twelve in 1728, eighteen in 1815 and settled at nineteen in 1904. You may be interested to read Canon Tydeman's humorous explanation of the Grand Steward's red apron.
Provincial Grand Stewards are permitted to wear crimson trimmed aprons similar to those worn by Grand Stewards, but with a two inch border rather than the three and one half inch borders which adorn the Grand Stewards' apron.
Whilst the pale blue used in Masonry is said to derive from the Order of the Garter ("Garter Blue"), the red, scarlet or crimson is associated with the Order of Bath. Universally, red is the emblem of faith, fortitude, divine love, magnanimity and, in its suggestion of blood, martyrdom.
In Freemasonry scarlet is an emblem of high dignity and is worn by one of the principal officers in the Holy Royal Arch. Crimson is said to imply "justice tempered by mercy" (perhaps because it is worn by high court judges?). Scarlet is said to represent "fervency and zeal". Wallace McLeod ruminates that since charcoal is sometimes associated in Masonry with "zeal", and "fervency" takes its root from the Latin word for "glowing, burning or hot", then scarlet would certainly be a good description of glowing charcoal! However to the members of the Hampshire and Isle of Wight Provincial Grand Stewards Lodge, the "red apron" will always represent service and a dedication to excellence.