Definitely identified the problem—I’ve run into this a handful of times…waving, calling, texting, jogging up behind my Uber ride and tapping on the window. Fun :) The color coding/unique symbol/flashing screen solution is a nice first stab, but could be iterated upon. Sheer daylight could conflict with the brightness of screens, weird reflections, etc. It could potentially make the experience more of a hassle than an ease.
The truth: It’s not that simple.
As I see it, the main point Jason focused on here is the beauty of product design—identifying DETAILED user needs and pain points, [insert your agile/lean/iterative process here], and finally implementing that great solution. I’m sure this isn’t the first time that Uber or Lyft have heard this. I bet the solution is something they’re still tweaking.