We have two pairs of these shoes for both my older kids.  My daughter has the ones that turn purple and my son has the ones that turn blue.  My daughter's shoes were bought first she was so impressed with the way they change colors in the sun, so when my son needed a new pair of crocs this summer, we ended up splurging on some for him, too.  (They're about $10 more than the plain old crocs.)  My son's shoes, which are only a month or so old, still work great, but my daughter's no longer change color.  It's fine because she doesn't really seem to mind, but I think for the extra that you pay for these shoes, they should work!  They just look dingy now.  At least they're functional, if no longer fun.