These granite pavers may look it, but they are not wet. The darkened perimeters are a form of efflorescence called crypto-florescence. Crypto-florescence is when efflorescence is absorbed into the pores of the stone. Because it is within the stone, it cannot be removed with acid cleaners. This defect is also known as 'picture framing'.
The source of the efflorescence is from the sand and cement bed beneath the paving that has wicked up between the joints and absorbed into the perimeter of each paver. This can happen with any type of stone or concrete paver.