Not knowing much apart from basic chemistry, and certainly nothing about cost of production or the reagents, I wonder why this US patent filed by Taylor (scroll down to example 1) for producing a liquid color change assay for CYA never came to market in the K-2006? Does it exist in any other kit?
http://www.google.com/patents/US7544517
Mike
http://www.google.com/patents/US7544517
Mike