Not sure what's going on about the colors, but if it isn't "in addition to its other types", it's better than a Plains. If it's like it reads, it seems too random. You want nonbasics (okay, some) to fix your mana. By the time you have six lands, this is totally irrelevant in a regular land.

If I want black or red, I'll just use the latest BR land. Even in a WBR deck, I'll probably want something else.

You know, I do find this intriguing. The doesn't untap thing looks like a control method for a minor splash, but I think the card reads better if it was simply a basic land that turned into another basic land once a number of lands was hit. Like SU mentioned, 6 may be too high. But, really, any number under that seems fair game.