My older daughter has used this brand for several years, and loves them.  So I decided to try them for my younger daughter.  She chose pink.  Unfortunately, after just one month of use, the upper soles of the flip flops (where feet touch them) have turned black.  They look disgusting!  I have tried every possible cleaning technique I can think of, to no avail.  I was able to lighten the black marks at the heel, but not at the ball or toe area.  I'm very disappointed at how they already look as if she's used them for years.  She doesn't run around outside barefoot, so I'm not even sure how they got such a dirty appearance.  I was never able to tell any problem with the pairs my older daughter has used, but I guess that's because they are black-bottomed and we can't tell.
On the up side, they are super comfortable.  Run a bit wide.  The sparkly straps and pink color were a selling point for my daughter.