NP-hardness conjecture for the maximum chromatic crossing number

For a finite point set in the plane and a red-blue partition, the chromatic crossing number is the number of crossings between an edge of $\operatorname{EMST}(R)$ and an edge of $\operatorname{EMST}(B)$. The maximum chromatic crossing number is the largest such number over all colorings. Maximum chromatic crossing-number conjecture. Finding the maximum chromatic crossing number of a point set in the plane is NP-hard.

The source poses this as a complexity question alongside questions about the possible size of the parameter and its relation to the EMST-ratio; no resolution is given.