Hair Coloring

I've been natural for three and a half years. Although i'm thrilled with the overall health and length of my hair, I have a slight problem. Slowly, but surely, there are a few grey hairs that are getting on my last nerve. Currently, I mask my greys by strategically parting my hair to cover them and another way that is too embarrassing to say. Right now, I have an incredible itch to color my hair so that I could take care of my greys in a more lasting way.  I'm hesitant as to what system I want to use because I don't want my years of good hair health to go down the drain by using a coloring system that could potentially damage my hair. I've done some research and concluded that I need a system that is ammonia and peroxide free. I came across Naturtint and Herbatint.

Both products claim: 

• NO MORE AMMONIA
• NO MORE SMELL
• NO MORE PERFUME
• NO MORE ALCOHOL
• NO MORE PARABENS
• LESS PEROXIDE WITH A NATURAL RESULT
• 100% GREY COVER 

I'M SCARED YOU'LL! I don't want to cause damage to my hair or alter my texture in any way but i'm tired of these greys. Have any of you used the products mentioned before or know of safer alternatives that can color my greys in a timely and healthy way? Looking forward to your recommendations.