Over 50 and Want Highlighted Hair Back to Natural

I have been highlighting my hair for 14 years and I am sick of the washed out blondish streaky look. I want to let my hair go to natural, which is a medium-dark brown, now streaked with gray. I don't mind the gray, but I'd like to try to change my hair back to that darker color, or some other close enough look. I'm 52, so I'm wondering if I should go very dark, or maybe just a little darker.

What looks best with 50ish skin? I look younger than my 50s (low to mid 40s).