
The nails are exactly the same – yet look pink in one picture and purple in the other – and it is all down to the background it appears on.
Sadly, this time there are no tricks of the mind, simply a rather nifty Photoshop trick that means the see-through nature of the picture allows you to alter the colour however you so wish.

http://www.unilad.co.uk/articles/just-when-you-thought-the-black-and-blue-dress-had-finally-been-forgotten/