In one of my other lives I was a hairdresser.. I'm actually licensed in several states.. Going natural is difficult for almost everyone. I started going grey very young.. probably had a few greys in high school.. not grey all over, just in a horse shoe aroung the top of my head.... I have a real "Jay Leno" look, you know, like I fell on a marker! so I've colored my hair for years and years.. I've gone from dark brown to light brown and now to sort of a medium blonde.. geeze this is a pain!
The easiest way I know to go natural is to keep coloring for awhile, lighten the color used.. then start leaving an area generally in the top/side uncolored.. each side of you head.. not at the hairline, but back a way.. as it grows, keep adding more and more so that you gradually go natural. I think its as much of a pain that way as just going for it and looking awful for a few months.. going to a medium blonde helps because it doesn't show the regrowth like a brown does.
To cut the yellow and give your hair a wonderful white color use fandiful rinse.. the name you need is White Minx.. It looks a bit blue in your hand, but doesn't leave any blue in your hair. It cuts the yellow and give your hair a beautiful white color. There are the purple shampoos too, but I'm not familar with any except the professional brands. They also work wonderfully.
I sympathize with you.. I've wanted to stop coloring my hair too.. the other problem when you stop is that natural hair has a different texture than colored hair.. so it acts differently.. talk about bad hair days.. cripes!