Why cannot the lego ultrasonic sensor sense clothes?
Is there a sensor that can sense clothes from medium/long distances (farther than color v2 sensor)?
Can the lego ultrasonic sensor sense tennis balls?

I've gotten the sensor to sense my arm while wearing a shirt or jacket, so this is interesting. The sensor works by detecting reflected sound waves, and the clothes may be dampening the sound enough to distort the results. Also, if the clothes have folds that are set at an angle, then the reflected sound may not be in the direction of the sensor, and again you may not get usable results. Try using an IR range finder sensor for better results. As for the tennis ball, I'm not sure, as I've never tried, but I did get whiffle balls to work.