Grimmjow does not abide by the color-coding set forth by the train. He's still wearing red, at least, but he's mostly just looking for things to fight.

When he hears the yell, he leaps into action. Not because he's worried about Wormmon (or Ken, but who cares about Ken? Not this cat.) but because he thinks, maybe, he'll get to fight something more interesting than a plant. Finally.

When he arrives, he's in his resurrección form, grinning wildly as he seems to drop out of the canopy, right at Wormmon. Where did his clothes go? That's a very good question. Probably in a tree. Hopefully intact.