Never wrap any cord or strap around your glans and stretch. That is a sure way to not only cut off blood flow completely to your glans but for sure your going to damage the nerve bundle on top of your glans. Those kind of pressures are killers and it is no wonder you got discoloration. Those are very bad practices.
When we hang we use a designed hanger that keeps pressures from the top and never allow the glans to be a carrier of stress. Does that mean that the glans don’t get cold? No, it does but we limit any hanging to 20 minute sessions and then restore circulation by releasing the pressure and perhaps even jelqing back in new blood. All the hangers you will find here at Thunders will be designed to clamp on the sides of your shaft only, so the nerve bundle is avoided and all the hanging pressure is applied on the sides of your shaft. The glans should avoided at all times.
Manual stretches can cause problems simply because they are applying pressures and pinches in very small areas. That will cause bruising which is where your discoloration is coming from.