popular redken shades eq forumlas?

I am a fifty year old moan with mid length hair. I am about 50 percent gray, maybe a little more. I have my hair colored every 4 weeks. Roots are done in 4n redden fusion and the rest is done in 75 percent 5g and 25 percent clear. I have olive skin and natural dark brown hair but not black. I do not like red hair but would like to add a little hint of something to this color to make the color more vibrant. I have a friend that uses 50 -50 5rb and 3rv and i really like her color, but her natural hair color is lighter than mine and she isn't as gray. Her hair looks like a deep brown and not red and is very vibrant and not flat looking. I would like to stick with the 5g but maybe add a hint of another color to make the color prettier, any suggestions on what i can add to the color? any suggestions on redden formula that are popular using shades eq for pretty brunette colors?