Quote "The colour doesn't matter so much. The middle one should be a ribbed white plastic cartridge type filter and this has a rubber washer at the top. The third filter is a different type of carbon filter and usually has a diamond pattern mesh round the filter to let water through the filter which is why it needs a washer top and bottom, so that the water goes through the filter and mesh." Unquote
Hi Dave
Not the middle filter, the third filter.