What 'power' do I put for colored contacts?

I cosplay L, and I'm buying black contacts to go over my irises. Whenever I try to buy them, it asks what power I need. Now, of course I'm going to choose 0.00, because that would mean there's no power in it. Right? I have absolutely no clue! D: 0.00 might be super-powered contacts!
I have good vision, so I don't need them. :I Therefore, I have no clue. xD
So do I just leave it blank, or put 0.00 for it, or what? D:


__________

Directory Submission Service|Social Bookmarking Service