Do you consider Colosseum & XD gen 3?

So colosseum and Xd are in the spin off section. But I would consider them gen 3 games because they can communicate with R/S/E and FR/LG, you build your own party, level up, explore a new region & clear a story. I think they're more than just a way to get gen 2 pokemon, I think they're there own gen 3 games, and good ones at that.

I always thought of them as gen 3 games rather than spin offs. What about you?

They are gen 3 games (becausr they were made in that period of time and communicate with RSE/FRLG to boot), but not main gen 3 games.

I'd say the main gen 'number' games are the ones on a handheld, made by Game Freak. While Colosseum and XD do basically use the same game mechanics, they're made on the GCN by a separate company (Genius Sonority), and have their own significant differences (lack of wild Pokémon/no real routes, Shadow Pokémon/snagging, vast majority of battles being doubles). Hence I'd still think of them as spinoffs.

My opinion is pretty much as they said before me: Both Colosseum and XD are spin-off games (really good ones though), yet both belong to the Generation 3 movesets and pokedex

They were made at the same time and they possess Gen 3 Pokemon only so I say yes, they were Gen 3.

They technically are Gen 3 games. I never really think of them to be related to RSE/FRLG, but that was because I never traded to those games (well only RSE, I don't own Firered or Leafgreen cartridges).