I think I sort of figured out why there has been some confusion as to the base color of the shirt.Last night I finally got to check out Dark Knight at IMAX (and of course, I was paying close attention to the Joker's wardrobe).For the most part, as best as I could tell, the background of the shirt did look like it was white - however, in the interrogation scene, the background color clearly is not white at all.Since most of the reference pictures of the Joker's shirt come from this scene - and it being the only scene we really see him without his topcoat on, the color of the shirt in this scene really made us second-guess ourselves over and over.The reason for the color variation in this scene could be several. The persperation from Ledger's body could have made the fabric look darker, or perhaps the shirt he was wearing was an 'alternate' version made by the wardrobe department because it may have looked better for that scene where most of his shirt was shown.My IMAX is over an hours drive from my house, so I won't be making the trek back out, but if anyone wants to double-check my theory, go for it.Going with a white base fabric is the best solution, because like someone else said here, the shirt can always be lightly dyed to get a darker color.Let me know what you guys think....