It may have been an evaporation line that looked like a positive, or the other test could have needed a higher level of hormone to show positive. Wait a few days and take another test, or get a blood test.
well i was told it didnt matter if it was light pink or dark. i would go to the doc and have them do a test.
Different tests have different sensitivities so may detect pregnancy at slightly different stages during early pregnancy (sometimes a few days apart)
Try taking an early response (FRER) with FMU. It should give you an accurate result.