What is the least harshest hair color that WILL work?

well, the safest hair color would be semi/demi permanent haircolours, but they don't lift so therefor you wouldnt be able to get the light brown you want, they only darken.. no hair color is least harsh than others, they all have to go into your cortex, which is the middle layer of your hair, so if your hair is healthy than go ahead, but if its brittle than i suggest waiting a couple months. go to a beauty supply shop such as sallys which is open to the public, cosmo prof (which you need a license for), and just ask them to help you pick out a 40 volume developer (40 is best for lifting the hair color, than 10 and 20, which are usually for darkening the hair) and whenever you need a retouch the volume bottols are good for many many uses, you just have to go to the store and pick up the brand of hair color.