I have darkish brown hair, and i want to put a few magenta or reddish highlights in it.?

is it necessary that i bleach the parts i want to dye? or can i just leave the dye in for a while, and it be like a dark red/magenta color. because i know the color will fade, and i don't want to redye it over and over again avoiding the fact that the bleached parts will turn gray or whatever. i rather it just fade and go back to my brown hair again. less hassle.