Well deductive logic tells us that since all the Yoshi's are a different color, if you have the green Yoshi, then you are playing as the "main" Yoshi. We should research to see if the the Yoshi's (in general) have the ability to change colors.

Good question. I really don't know if Yoshi's always the same Yoshi or not.
I like to think he's always the same except when he turns into a different colored Yoshi :)

they are the same but different colors

Dunno. I mean they all come in different colors

Hard to say. I think its the same becourse all the other chaters is friend with it, and then it need to be the same. But its maybe not the same becourse they look alike. But i mostly think its the same becourse it maybe not was the same bowser or toad. So i think its the same. (dont know)

Well, the green Yoshi is the main Yoshi. They come in a variety of color

IT'S ONE YOSHI THAT STARS THOSE GAMES. I THINK THERE IS ONE OF EACH COLOURED YOSHI.