Right. Because First Need is a carbon filter, dye bleed-through means one of three things: 1. a mechanical failure causing the water's path to short-circuit (bypass) filteration or 2. the carbon is saturated and has started desorbing (sloughing off) organic contamination or 3. you're pumping too fast for the filter to adsorb the dye (which could potentially occur with a brand new filter, depending on the maximum pump rate).

i.e., If you see dye discharge from a First Need (or a Hiker or any filter with carbon) you know there's a problem. If scenario 1. pathogens will make it through into the discharge. If scenario 2. pathogens may still be captured, but your cartridge has adsorbed all the carbon its capable of. Unfortunately, just by observing color you can't know which.

With a filter that doesn't use carbon, nothing of value is learned via the dye test. It's not a measure of the filter's effectiveness against pathogens.

“however just remember that it's not really a valid test for filtering pathogens, or for checking for a
cracked filter.”

So First Need and all their engineers and scientists have been wrong all these years?
It appears they have a pretty slick method for finding an internally damaged filter.
From http://www.generalecology.com/first%20need%20original%20instructions.pdf

“A simple test to assure that the canister has not been damaged internally, either during use, transport or backwash is to:
1. Add a couple drops (no more) of ordinary red, green or blue food coloring to a glass of water
2. Pump this solution through the canister.
3. The filtered water should be colorless.
If the filtered water is still colored, even faintly, the internal canister matrix has most likely been damaged and THE CANISTER SHOULD NOT BE RELIED UPON UNDER THIS CONDITION AND MUST BE REPLACED.”

There’s a lot of good stuff at their Q&A: http://www.generalecology.com/qa.htm