You can't see thru a fuel filter, think about it, it's a filter... If you can see thru it then fuel can go straight thru it, eliminating the filtering process. Fuel is forced thru the filter by pressure, it's a paper, or like material for the actual filter. Try blowing thru it, it should barely allow your air thru, and it is a cheap fix. Replace it.
It is a bad thing if you cannot see through the fuel filter when you hold it against the sunlight. You need to clean the filter so as to avoid clogging as small impurities can lead to this. You can get directions on how to do it at http://www.ehow.com/how_5117221_clean-fuel-filter.html.