No hair color execpt a rinse will completely wash out.Demi color and permanent is 2 different things. There is basicly 4 types of hair color.permanent,demi, temporary and rinse.If you are now using a perm.color and want to try to go natural, demi is a step in that direction.AlthoughI do not like or use demi color,You will have to retouch as often as it will fade off and roots will show.But the up-side is you will be growing and cutting the permanent color off and can lighten ,because we lighten naturally this softens our looks as we get a little older.Maybe you could do one of those little short cuts and get the younger edge.You are on the right road, Be careful in color choice as you already know if you color.Color on color can be darker than you intended.Another idea is getting low lights in a lighter color than you use now and blend into your color. This can help while you are growing off permanent color.Keeping a younger image and growing color out graceful is best in small steps if you do it yourself.You can go into a beauty supply house and they will offer their advise and advise you on products.