MS can certainly implement a multi-color LED on the charger if they wanted to--and hopefully they do; it would be a great feature.
The battery indicator LEDs on my ThinkPads turned yellow when you got below a certain threshold. This had saved me several times when I thought I had plugged in the ThinkPad but did not; or when one of the power cord connections was not snug. The end result is that the laptop was not charging and, over time, the battery indicator changed from green to yellow and that's how I was able to detect and correct the problem.
One is not always on one's PC doing something such that one can glance over into the system tray to see the charge status. The multi-color LED charge status is especially valuable under such circumstances.