Wow, this piece is so cool!!! I LOVE how it came out! You did a really amazing job drawing them all! I especially love how you drew Sceptile and Charizard! This is a really well done piece! Awesome job!
That Kabutops in praticular is an old OC of my friend by the name of Kronic. The reason the Kabutops is Purple and Orange is mostly a reference to Pokemon Mystery Dungeon 2, and it was mostly a inside reference in our fanmade PMD MMO by the name of Pokemon Mystery Universe.
Long story short, the reason why he is that colour is because he is a "Primal" Kabutops. It is a reference to how Dialga (spoilers; one of the major antagonists of PMD2 in the main story) was in a "Primal" form. I believe the games explination for this form was that Dialga essentially went into a mode of rage, and lost all thoughts of reason... Going down to his bare essentials of survival.
The significance of this was that the colour pallet of Dialga changed to mostly Purple and Orange. Well... In our PMD MMO at the given time (this was about 4 - 5 years ago), the concept of "Primal Pokemon" was a huge idea/fad that everyone was into... So we had all these recoloured pokemon sprites that were all Purple/Orange (Or just a darker variant of said pokemon). Of the sprites that we had, he chose this one.
It eventually turned into an OC that he used in a long roleplay series called "The Crew"... The whole series is several hundreds of pages long X_X But yeah... That is pretty much what is up with that Kabutops. He is a very close friend of mine (heck, everyone who appears in this picture is a very close friend of min, haha).