Thanks Jan! My little secret...I airbrushed the whole tank in Tamiya German Gray, then did panel fading with progressively lighter shades of the same. When all was dry I applied a glaze of acrylic Citadel Blue thinned with water. This blended the gray shades and gave a blue-ish hint to the gray. Then black oil pin washes, dry-brushing, and final pin-point highlighting with a white pencil. And, of course, good old pigments!