First time wanting to color

hello, I'm 37 male and while I have a fairly small percent of my  hair now white (scattered all over), I've never bothered coloring.
My hair is very dark brown, straight, light and I do have a bit of hair loss (not chronic).

My fiancee is asking me to have it colored, so I've agreed, but do have some concerns:

• By using hair dye, will it make my black hair start going white at a faster than normal rate?
• Would hair dye damage my hair
• I'd like my hair to look natural and should not show that I'm coloring
  
• I'd prefer to use non-permanent as it would fade-out instead of showing a marked difference at the roots as my hair grows.

I'd really appreciate some advise on this.