Here are a few thoughts, as I've studied this issue for many years. In fact I have a presentation I give on this subject as part of the ACM distinguished lecturer program and the IEEE Computer Society's distinguished visitor program. 1) There actually have been academic programs called computer science engineering, but the name never caught on.
The color black represents strength, seriousness, power, and authority. Black is a formal, elegant, and prestigious color. Authoritative and powerful, the color black can evoke strong emotions and too much black can be overwhelming. In heraldry, black is the symbol of grief.
Purple was the color worn by Roman magistrates; it became the imperial color worn by the rulers of the Byzantine Empire and the Holy Roman Empire, and later by Roman Catholic bishops. Similarly in Japan, the color is traditionally associated with the Emperor and aristocracy.