"Grays" is the term used for the gray uniforms worn by Herald-Trainees. As with all Collegia uniforms, they are a subdued or washed-out version of the uniform worn by those who've graduated. In this case, the gray is a subdued version of Heraldic Whites.
Grays are made of hard-wearing canvas material.[1] They are not custom made for each trainee, as a child will quickly outgrow them. The Collegium keeps a stock of average sizes, and swaps them out as the children grow.
"Spoilers"[]
Alberich, a soldier from Karse who was Chosen as an adult, ended up with a darker gray version. They needed to tailor uniforms for him, and they were out of the regular color. He was pleased to have a less visible uniform, and continued to wear his dark grays after his internship, unless affairs of State required him to wear the standard "shoot me now" Herald Whites.[2]
When mercenary Captain Kerowyn was Chosen, she immediately adopted the same philosophy.[3]