Why is this Einstein ring pink?
OK, guessing rather wildly in the absence of solid information....

The press-release page is here; that provides a bit more information
than the news article, and includes two images of (different regions of) the cluster and a hint that the cluster is named MACS0940.

I think the main image is a color composite from HST imaging. It shows a galaxy cluster (the yellow galaxies). Also visible is light from an Einstein ring, the gravitational lensing by the cluster of a (single) distant background galaxy. The thin, white, ringlike streaks within the pink arcs are the stellar light from this galaxy (probably UV light from massive, recently formed stars); the broad pink arcs themselves are (I'm guessing) the Lyman-alpha emission as seen by MUSE. (So the image is a composite of both HST data and MUSE data.) Thus it is plausible to say that the Einstein ring is made up of stellar light from the background galaxy and (in pink) emission from gas in and around that same galaxy; the assumption is that said gas is mostly in a halo around the galaxy.

The second "magnified" galaxy referred to in the news article is probably in a different part of the cluster, and doesn't form a nice Einstein ring; it is presumably the four pink blobs in the second image on the press-release page.

This is the abstract for an HST proposal on which Claeyssens was a co-I; the data were taken on May 1, 2019, so it's plausible the image is from those observations:


  Recent deep integral-field spectroscopy observations using VLT/MUSE
  revealed two     high-redshift (z>4) lensed arcs in the galaxy cluster
  MACS0940. Notably, both lensed galaxies show highly extended
  Lyman-alpha emission (> 5 arcsec)... one of these galaxies forms an
  almost complete Einstein ring, with the Lyman-alpha arc reaching an
  unrivaled extent of 30 arcsec.