The idea is great. Currently someone has to go to a clinic, have a test administered, then wait a couple of weeks for the results. With this condom, you can get an early indication of... issues. For me, if it changed color, that would be a good indication that I will never have unprotected sex with this person and would know to disconsider them as a long-term partner.
Really, your post gives the impression that you don't know much about how sexual relations work. Using a condom with someone who potentially has an STD does not "defeat the purpose", it is the purpose. It allows you to have sex with someone whose infection status you're unsure of, without getting the infection. If you know someone is clean, you don't need to be dealing with condoms in the first place.
I won't pretend to be some kind of playboy, but it should be apparent that most relationships start out more like 1-night-stands than arranged marriages. There's usually not a formal interview process including STD test before the first sexual encounter. Hell, there's barely time to even get a condom on. This product would be a godsend for slowing the proliferation of STDs. Regardless of your strategy for obtaining sex, that's going to benefit you.
