grecian 2000/Just for men - whats the differences?

Women have such a huge variety of Hair dyes in various different brands, yet for men all I see a 1 bottle of Just for Men or Grecian 2000, well why is this, i mean dont men have different colour hairs too? and what is the difference in these 2 brands?

ive got black hair so how i can hide my greys?

thanks x