I had about 80 karts on GT5 (about 16 different colors for each model), hoping to repeat it on GT6, and here's how it worked:
My white karts are #19, for Ayrton's Toleman-Hart;
My black, yellow and red karts are #12 for Ayrton's Lotus-Renault, Lotus-Honda and McLaren-Honda;
Some of my other red karts are #27 for Ayrton's McLaren-Honda, and some are #1 for the same reason;
Blue karts are #2 for Ayrton's Williams-Renault;
And then, most of my remaining karts and practically all of my numbered cars are #8, in homage to Ayrton Senna, and in tribute to his shows at Brazil, Donington Park (the most amazing first lap in history), Monaco, Japan and Australia, all in 1993.
Sometimes I use #5 on blue karts to homage Nigel Mansell.