How do I get a random color and dim it down or make it brighter?

def DimmColor(dimmer, randrange):

    rgb = [0,0,0]
    randomed = randrange(1,1531,1)

    m = int(randomed/255 - (randomed%255)/255+0.1)#0.1 corrected "tolerance"

    what_plateau = ((-m+2)%3 +(m)%2)%3 #2,2,0,0,1,1
    what_terrace = -(m%3 +(-m)%2)%3 #0,1,1,2,2,0
    what_slot = (-m+1)%3 #gives rgb[slot] slot=1,0,2,1,0,2
    increase_decrease = (m-1)%2 - m%2 #toggles plus and minus to get all finite rgb colors. Increase decrease under terrace. 1 -1 1 -1 1 -1
    factor = m%2 #subtract or not. 0 1 0 1 0 1

    n = int(randomed%255)
        
    rgb[int(what_terrace)] = 255
    rgb[int(what_slot)] = int(255*factor + n*increase_decrease) #Combined alternates +inrease or -decrease +green -red +blue -green +red -blue
   
    if dimmer > 255:#0 to including 254 darkens. 255 changes nothing. 256 to incl 510
        rgb[what_slot] = int(((255-rgb[what_slot])/255)*(dimmer-255)+rgb[what_slot])
        rgb[what_plateau] = int(dimmer-255)
    elif dimmer < 255:
        rgb[what_terrace] = int(dimmer)
        rgb[what_slot] = int((rgb[what_slot]/255)*dimmer)
    elif dimmer == 255:
        pass
    else:
        print("dimm dungeons revolt")
        
    return rgb