And with "do this for me now" use cases, quite common for phones (such as "did someone just tell me something relevant in that message I just got" or "what was that building number again?" while walking down a street thinking about some larger goal), I find visual clarity all the more appealing. So "plain" might be just what the use cases call for. Several icons or buttons all made to be 3-d and pretty with candy-round edges and bright colors, each wanting to impress me with slickness or compete to stick in my memory better are just more distraction from that one shape or word my visual cortex is primed by the task to find.