Skinny, dark line on pregnancy test?

just took a pregnancy test, the + / - kind, waited about 30 seconds and figured it was negative, went back and looked at it later and there was a skinny, DARK blue line running through the -. Is this a positive?? I know probably read it after the suggested time but Ive been reading about evaporation lines and it says FAINT lines will show up, this is a DARK blue line, but skinny... do the tests sometimes take a minute or two to show a +? I only looked at it for 30 seconds then thought i was in the clear.....???hmmmm