“I'd be willing to bet, but haven't proved by actually doing it, that it's the activated charcoal/zeolite or other organic bonder (it isn't all charocoal) and I could make something with fish tank zeolite or the like that will remove the color, but not have small enough pore size to stop the pathogens.”

That would be interesting to see. The Hiker Pro should at least have that quality (to remove color). Maybe they need to experiment more with their activated charcoal.
Likewise, if the First Need did let color through, I would not use it. If it doesn’t, I would trust it because the engineers at First Need have been doing this for 25+ years. I wholly trust their food coloring method. I do not trust the food-coloring method with any other filter (yet). This makes testing the filter integrity so simple.
First Need has been independently certified by several sources. http://www.generalecology.com/testcenter.htm
A typical conclusion is as follows:

“CONCLUSION
It appears that this technology is capable of meeting the test requirements as a microbiological water purifier as defined by the EPA(4) without the use of chemical disinfection. The small size, lack of external power requirements, and high degree of portability of these units make them suitable for recreational enthusiasts who obtain their drinking supply from rivers, lakes, or other untreated water.”

http://www.generalecology.com/wemedmag.pdf

Also no lawsuits is a good sign after 25 years. First Need guarantees:
“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.”

-Barry