Very nicely done, lovely grain matching. As to the colours,if your camera has some exposure compensation adjustment you might try giving a little more exposure and your white background will appear white. Usually there is a setting where you can increase by say +1. Just don't forget to reset it afterwards. What happens is the camera meter reads the average light level and white is in effect seen as grey. Compensation resets white to white. There are other ways to do this too but simple is often best.