For starters, 512 claims in the lawsuit it's a cheap trick for 818 to copy its schtick by using an area code for its moniker. BTW ... 818 is the San Fernando Valley, and 512 is Austin.

But, there's more ... 512 claims the color scheme on the 2 bottles is so similar, it's meant to confuse consumers. And, 512 adds, it was in the game first ... since 2015.

Check it out for yourself ... when the 2 bottles are placed side-by-side, they do look similar, both in color and design.

Now here's the twist ... 512 zeroes in on Kim Kardashian in the lawsuit, claiming something shady happened when Kim's app, "Kim Kardashian: Hollywood" was promoting Kendall's 818 and for some reason the 512 bottle was front-and-center on the in-game images. It's unclear if this was intentional or a mistake, but the irony ... a mistake would be even worse because it validates 512's claim that people are easily confused.

In screengrabs from the game, you see a bottle with a similar shape to 512. 512 claims they reached out to game creators after first noticing the product in the game, and it was then changed to the green design ... and it appears the bottle made another change to yellow.

As it was put in the lawsuit ... “Either Defendant intentionally used Plaintiff’s bottle, hoping to further blur the lines between the two products, or Defendant was itself confused about the difference between the two brands."

Kendall was not named as a defendant ... only the company is being sued. A company rep says, "We are reviewing the complaint and believe the allegations are without merit."