You mean your labia, correct? Your vagina is the muscular tube insude you (where your menstrual blood comes out), while your labia are the "lips" of your genitals. There are inner labia, called labia minora, and outer labia, called labia majora.
For all about female genitals, please check out Pink Parts – Female Sexual Anatomy.
Labia come with immense variation: it is normal that your labia can be of different sizes and different colorings or texture. - So it's highly likely all is fine and dandy with yours. Stop your extra efforts of trying to clean the labia that seems darker. - The skin on your genitals can be a few shades darker, pinker or redder than your skin anywhere else, and it's normal that some parts are more intensely coloured than others.
Many girls unfortunately worry about the appearance of their labia, even though they are perfectly fine and well.
KittenGoddess and I had a project in April all about labia: we held the second international labia blogathon, where many girls of all backgrounds and ages (and a few men, too) shared their labia positive thoughts: check out http://labialove.blogspot.com
"it may look like i'm moving but i'm standing still."