@Gkikas-LGPZ Yes, it uses Schmidt-Appleman chart criteria; the colours indicate where the flight level falls. We are working on writing the live documentation to explain the colours and numbers in more detail, and we aim to have that done by the weekend.
It runs on whichever model the user has selected. During our testing, the results appeared to be consistent between the models. However, over the last 24 hours, ECMWF and UKV have been significantly different. So, this is something we are looking into.
Persistent contrails linger in the air, slowly spreading and forming cirrus-like clouds. (Cirrus homogenitus) There is a definable temperature, pressure and humidity when the ice crystals in a contrail can no longer sublimate and remain floating in the air.
We will define the definitions properly in our soon-to-be-published documentation. Now we are getting some worldwide feedback, we will probably have to make the descriptions a bit more vague - Long contrails - possibly persistent) to allow for model inaccuracies.