How many shades of purple are there?
Purple is a combination of the primary colours Red and Blue. Given that there are many shades of those two colours, there are probably more shades of purple than you can imagine. Also, different paint manufacturers give their own names to their paint colours, so the same shade could have many names.
Here is a link you can check out http://greensleeves-hubs.hubpages.com/hub/Shades-Purple-Greensleeves
Your best bet on deciding a room paint colour would be to go to a store that specializes in paint, or even to Canadian Tire, Walmart, Home Depot, Home Hardware, or RONA and check out the paint colour sample cards. They are free to take home and put against your wall to get a better idea of what the colour will look like in your room.
Have fun decorating :)