Modern user interfaces tend to use “flat” visual style of user interface, where buttons, text inputs and other controls are designed in a minimal manner with solid backgrounds and borders.
Previously, the pseudo-three-dimensional look and feel was popular to imitate the physical origins of these controls. This approach is called skeuomorphism.
While flat design is less cluttered and is easier perceived, there is multiple evidence, that it can result in less affordance of the user interface. The users simply need more effort to recognize buttons and inputs and distinguish them from emphasized text labels and other non-interactive elements of the UI.
The easiest method to support the operator is to define a unique visual style for inputs, buttons, and other controls and support it consistently across all user interfaces without exceptions.
For instance, the buttons can use solid background fill with unique color associated with them. But it can be difficult to achieve with complex user interfaces that have dozens of elements.
So, it can be optimal to combine traditional skeuomorphic and modern flat design — the buttons may be designed with linear gradients and drop shadows, while inputs are designed with inner shadows and borders. Actually, some modern operating systems and mass-market UI frameworks already use elements of this approach.
This will make the recognition of components much simpler, so will decrease the overall perceptual and cognitive load.