Summary: Google's Material Design language reinforces one of the most valuable principles of graphic design and user experience: provide design elements that make it clear that a control is present for use.
The Problem with Clean UI's
UI's that are so clean, are invisble! Hiding UI elements is one of the worst things a designer can do. But the motivation is understandable: clean up the interface, reduce the clutter, simplify! These are all extremely important goals of UX Design and Visual Design, two overlapping efforts that go into design.
Image above: This playing card from our new UX Certification training (fresh dates to be announced in 2018), captures a key Material Design point: "Signifiers over clean". Clean is spelled with a K as in "Mr. Kleen" (a popular American kitchen cleaning spray) to remind us of the abrasive power of being clean.
An example of "clean can be too so clean, that it wipes out the UI" was found on Skype (Note: It's recently been updated to be docked in the top right during a call). For years, you could ask any heavy Skype user about Chat and they will tell you, the other callers could never find the chat element (it dissapeared when on a call, requiring mouse over, shown below, then click icon to open). Instead, it might have prompted the person you were sharing a link with, to auto-open instead of making them hunt.
The fix for providing a Clean UI
A signifier is a UI element that signals or invites usage. In the Interaction Design discipline, it is also known as an "affordance". A clue that affords or bekons usage, without requiring the user to think, study, interpret or play. In Google's material design language, they recommend offering clear targets and making UI's provide clear visual clues that a control exists. This mean NO HIDING controls!
Google is very clear in their Material Design guidelines: your visual design is useless without strong affordances (signifiers) present. This advice is underlying much of Material Design and for good reason, Google has made the mistakes: eg. Android was a grand unintended experiment in mobile usability.
Getting "clean" right is not trivial and requires getting past the following obstacles:
1) Your designer's brain (you can handle a lot more visual ambiguity than you realize). eg. Gray on gray doesn't bother you, does it?
2) Your stakeholder's opinions (visual design is so subjective that a UI signifier can be removed in one design review, all in the name of Klean. (You know who you are!)
3) Your user's brains. Users don't look at UI's and they don't care about rules or requirements, sequences or flows...let alone clean UI's. They care about doing what they want to do with your UI.
The best way to test your design to see if it's user-proof is with usability testing: watch users as they complete their tasks and see if they can find your UI underneath all that "clean".
To learn more about other approaches for testing Visual Design, check out: