Motorola G5 3GB RAM variant is available in 2 different colors - Lunar Grey and Fine Gold.
Yes, you can update this phone. However, this phone comes with latest Android 7.0 Nougat out of the box. So, you may not require to update the phone immediately.
No. Moto G5 does not have front camera flash but the display flash is there, which is as powerful as LED flash.
Motorola M5 has Water-repellent nano-coating for protection against water.