I think that, when the idea of World Tour came around, Millar thought it would be a good oppurtunity to change things up... You know, change things around so that it would be more interesting for him. He's done this in the Ultimates, too... He's made obvious characters in all of the books he's written. For example, in Ultimates 2 #1 there was a mugger that went after Steve and Janet. If you look at the dialogue, it's the token street hood, really. He's done this with the other characters, too, by giving Tony a tumor and a drinking problem, having Steve have such a problem with the modern world in a quirky way (I know this is a stretch because it is in his character), and Colossus was portrayed as the person in the corner among others because he thought he was different (You know, aside from the fact that he is a mutant). Millar writes right wing characters to make his stories more "compelling".
So, to answer your question, no I don't think Colossus was meant to be gay. He was in the Russian Mafia, for cripes sake! I really don't think they'd be too accepting of a homosexual among them... I do think that Millar changed him up a little bit to make a story and to make yet another character. It's like he was casting a reality show. You need to have blatant stereo types to make a show... That's what Millar did and is doing.