Does anyone know why the bumpers of the Porsche racing 914 had a two-tone font bumper (left and right side)?

Is the back bumper the same way?

Because it looks really cool.

It was because they ran two similar cars at an event once upon a time.
and they wanted a manner to tell the 2 cars apart so they would know whom was pitting, etc.

a subtle way to differentiate between 2 cars painted the same....

(why couldnt they just look at the number? LOL)

Yup.... A way to quickly ID a car coming at you on the track. As a crew member on the track sideline, you can't always see numbers on the bonnet or side of the car because of your perspective... But when half the bumper coming at you is an obvious color contrast you can tell who it is. It's all about easily IDing a car.

why - never thought to ask - just followed the trend : )

Then I guess there would be no need to do the back bumper.

I always thought it was to look more menacing... kinda for the same reason that William Wallace painted his face two tone before battle...

The big dogs used a variation in their livery colors as well.....note the stripe differences on the pictures below. Porsche also used card suits (clubs, diamonds, spades) on the nose of their 908s for pit recognition. 908s also ran with 1, 2 or no "arrows" over their bodywork, to the front of the car.

because when you're in the pit and the car comes straight at 'ya, you can't read any numbers ...

when you have 3 signal orange 914-6 GTs come into the hot pits at the same time, you need a sure way to tell them apart in a split second ...
Andy