The dark scheme came about after the display Tucano at CFS was painted all over dark blue for the 1993 display season. it suprised everyone that it was often the only aircraft that ohter pilots reported seeing. As there was a discussion at command level about the Support Command clour scheme at the time, this fact was mentioed and some trials were held to assess how much more visible it was -which proved it was a good colour for added visibility.
Hence the gradual change to black.