The latest Windows 10 Insider Preview Build brings (amongst other things) less colourful icons – more white. The Windows Explorer and Windows Defender applications are now represented by mostly white colored icons.
Seems like Microsoft is still forgetting about the blue Microsoft Edge icon. Just like the Store or calc apps, the “e” is white in Start Menu so different color in taskbar makes it less consistent.
Update 2016/05/30: Few days passed and the yellow color of Windows Explorer is backed.