Piste difficulty is based on the OSM field piste:difficulty (https://wiki.openstreetmap.org/wiki/Key:piste:difficulty), however, the corresponding colors differ per region. It seems that the pistes are drawn using the US/Canadian colors. This is confusing in European resorts.

For example on the Kitzsteinhorn: https://www.strava.com/maps?sport=WinterLike&style=winter&terrain=false&labels=true&poi=true&cPhotos=true#15.79/47.21517/12.699328
 

• Black Mamba(advanced) should be black, is shown in red
• Langwiedpiste(intermediate) should be red, is shown in blue