About dyes...I guess it depends on the dye. First I have to say if the color you are using will lighten your hair, then that will damage it. Bleaching hurts our hair. If you have stronger hair than I do, then it might be able to take it and not break off. My hair would break back in the days when I lightened my hair. If the color you are using is making your hair darker, or adding a tone, if it's permanent, it still uses strong chemicals, and will cause a bit of damage, but not nearly as bad as lightening. A demi-permanent color damages your hair very little. Temporary coloring or a rinse shouldn't damage your hair at all (but it depends on the ingredients they are using--check for hydrogen peroxide and/or ammonia. These are damaging).

I guess whether you should dye your hair is a matter of what is more important to you-- or which one you would enjoy having more: the color or length. If you have short hair and are planning on keeping it short, then lightening or coloring is okay, because you will be cutting off the damage before it gets bad anyway. But if length is what you want, if your hair is as fragile as mine, then it's best to do nothing that can possibly damage your hair.

So to be safe, it's best to use a rinse, or demi-permanent. If that isn't enough to work on your greys (if you have them, that is), then try a color as close to your natural color (or not any lighter than your natural color) as possible is best. This is because those shades closest to your natural shade won't use as much peroxide to lighten your color as a shade much lighter than your natural color.