Well, it doesn’t actually distinguish red from green, but it does indicate the amount of redness in red, orange, and purple objects by a series of stripes superimposed over the object. The Red Stripe app uses the device’s camera to view the objects in question and overlays stripes on those objects with a red component. The more red in the object, the more intense the stripes will appear to the app user. The stripes will not appear on blue or green objects. Since a person with red/green deficiencies can still see blue and yellow, the stripes will help distinguish which of two grayish objects is red. The Red Stripe app is available for iOS devices and for Mac computers. The iOS version of Red Stripe ($4.99) would seem to be more useful because it is portable than would the Mac version ($4.99), in my opinion.