The Waffen-SS only permitted Waffenfarbe other than white between 10 May 1940 and 5 November 1940. They had stipulated a wear out date on incorrect waffenfarbe caps of 12/31/40, but they quickly switched back to only using white on visor caps due to the expense and difficulty of troops having to get new caps with each change in assignment, which was very common in the Waffen-SS as it rapidly expanded from one division (SS-VT) to many divisions. However, after the RZM lost exclusive rights to produce this headgear in 1941, people could get anything made up by a capmaker if they had the money and could get away with wearing.
Also, as a side note, lots of these caps have been faked over the years due to their extreme rarity (and the huge profits made from converting a white piped cap to a colored piped cap). So watch out!