A big +1 on what "Scut Monkey" said. Checking a sanitizer visually is akin to determining the end of fermentation by looking at the wort. If you like these methods, you'd probably also enjoy Las Vegas.
Pragmatically, I put aside most of a gallon jug of Star San solution last Fall when I quit brewing for Winter. When I checked it in the Spring (yes, Virginia, with pH test strip) it was just peachy-fine, < 3 pH. I might note that I mix Star San only with the RO (reverse osmosis) water from the supermarket, due to the high concentration of calcium and iron in our well water.