In my view it makes no sense for the wavelengths to shift through the spectrum from red to blue if the effect is gravitational in nature.
But it makes perfect sense if the effect is related to the energy level of the material, just as metal radiates from the red to the blue regions of the spectrum as it gets hotter.
And given what we're seeing in the area of photonic metamaterials, it makes a lot of sense that the gravitational effects are being generated with greater intensity as the activation energy of the metamaterial is increased - the two are directly related:
“Electromagnetic stress at the boundary: photon pressure or tension?” Shubo Wang, Jack Ng, Meng Xiao, and C. T. Chan, 2015
https://arxiv.org/ftp/arxiv/papers/1510/1510.06227.pdf
“Electromagnetic stress tensor for amorphous metamaterial medium,” Neng Wang, Shubo Wang, Jack Ng, 2018
https://arxiv.org/ftp/arxiv/papers/1801/1801.00942.pdf