Well if you are worried about thin hair, having it darker makes it look thicker straight away, its just an illusion created by the darker colour. Also, for the first few weeks of colouring your hair is thicker because it is coated by the dyes, and has a strong shine. Maybe try a semi-permanent that way you can try it out, and it will be ok for you to repeat it once a month to keep the thickness if you like it.
P.S. despite the strangeness of that photo, I think it would suit you fine, according to your skin tone.
Oh and P.P.S. I agree with Cindy Crawford's theory of dark circles. It looks womanly and spiritual and interesting. I have a half-Indian friend and she has these amazing dark circles all the time and she looks so soulful.