Possibly calcium carbonate. Ellforescence is the term. They should fade with time with being in rain, etc. Someone here can explain better, and if there’s a way to remove it (or if I’m way off base!).

check this link for removal info: http://www.concreteconstruction.net/products/decorative-concrete-surfaces/what-causes-efflorescence-and-how-do-you-remove-it_o

I agree with the answers above, though I will say sometimes it is near impossible to remove. Ironically enough I was looking at a job yesterday where we decided the easiest route was just to replace them. (just as long as the new pavers don’t do the same)

When we had a new pavestone patio installed, the crew used a polysand. Instead of using a leaf blower to remove the excess sand, they used water instead which made the stones look hazy and bleached out. There are cleaners available to clean the surface, but I would hire a company to clean it for you.