One thing with Poser textures, make sure you change the highlight color from black to white, this might be what is making them darker but I'm not sure, I haven't had any trouble with too dark Poser textures so I'm not sure what's going on with that. A note on the textures, even making them seamless doesn't mean that you won't notice the tileing, your eye will naturally pick up on the repetitious nature of the textures and realize that it's the same texture repeated. Sorry I couldn't be more help, it's hard to give advice on how to improve an image, especially when you don't know what the artist is going for as far as mood and feel, which are entirely subjective for most people.