That bike was already mentioned here: http://www.schwinnbikeforum.com/index.php?topic=22887.0
Silver Mist ('71) was a one-year only color on the Sports Tourer, and is fairly rare.
One interesting thing about the Sports Tourer is that there were more one-year only colors than there were colors available for multiple years. Besides Silver Mist, other one-year only colors were Burgundy ('71), Kool Orange ('71), Opaque Green ('72), Sunset Orange ('73), Opaque Red ('74), Sky Blue ('75) and Lime Green ('75). From what I've seen the '71 and '75 one-year only color models are the rarest and most desirable. Bearing this out the highest selling prices for Sports Tourers that I've seen were mint '71 Silver Mist ($1100 in 2009) and Burgundy ($750 in Feb. 2012)
The only Sports Tourer colors available for multiple years were Kool Lemon ('71-'75), Sierra Brown ('71-'72), and Opaque Blue ('72-'74), with the Kool Lemon and Opaque Blue being the colors most commonly seen.