I don't even actually know how to cheat. Is it done with an emulator or a gameshark or something like that? I don't even really know what either of those things are, to be honest :).
I do remember maybe 12 or so years ago back when I was playing pokemon Blue, my little brother taught me the cheat where you go to Cinnabar Island, surf up and down next to the gym, catch the missing no. pokemon, have the rare candy as the 6th item in your inventory, go visit that guy in Viridian City....Something like that. To be honest, I don't even really remember. At any rate, I used the cheat for fun one game to level my pokemon to 100 and duplicate master balls to catch multiple legendary pokemon.
But really, it wasn't a big deal. I only did it that once for fun, and I didn't really think of it as cheating, because I restarted that game all the time and I didn't always use the duplication trick. Just when I was bored for something to do. It's not like I ever traded or battled or competed with anyone outside of the game, so what did it matter?
The only time I have actually "cheated," I guess, was to get my pokemon in Emerald up to level 60 so they could match the other pokemon's levels in the Open Level bracket of the Battle Frontier. Usually they are early to mid 50s in level after defeating the Elite Four, and it's a pain to grind levels, so I just feed them rare candies so I can play in the Battle Frontier. I don't really see that as a big deal because again, I'm not competing with anyone but the game, and the Rare Candies certainly don't power them up at all. Regular levelling probably would make them more powerful, if I understand EVs properly.
The only times cheating would never be okay, in my opinion, is if you battle with your friends or in competitions with pokemon you've taught illegal moves to....Even then, shinies and whatnot are fine, as long as you don't pretend you caught the shiny in a random battle. Who cares about coloring, anyways?