Bright 'permanent' colours do tend to fade i've noticed. However, one of my friends manages to surprise me sometimes.
She's had a semi-perm red box dye stay red over her light brown hair and she had to grow it out.
She then had bleached hair, and put a permanent (schwarzkopf Live XXL) red over it, and it turned out very bright, and faded to a bright pink. She then put on another Live XXL dye in purple, and it came out pretty damn bright, and stayed that way till she went over it with ANOTHER Live XXL black-blue, which turned out quite blue. She seems to be an exception to this rule of bright permanents fading.
Then you move on the the professional lines of bright hair colour, like joico and pravana. Pravana has a good reputation of lonevity, that it is basically permanent (and doesn't bleach out!) but it isn't mixed with peroxide. I've heard a little about redken high fusion dyes, which are mixed with peroxide and are bright colours, but don't know much about them.
Basically i think with how long the semi-permanent veggie dyes can last, theres not point making a permanent that will fade in the same time.