CindyJS

Conic by one polar pair, two points and one line

You should not be seeing a red line in this example, since it should be covered by a green line in the same location.

If the cyan point is located on the green line, this gives you access to conics which touch a given tangent in a given point of contact.

In this configuration, moving the bottommost point will cause the conics to switch roles unless avoided by complex tracing.