Why is there no color shift on the photo of the M87 black hole? Last year, the first photo of a black hole in Messier 87 was published:

(Source: EHT)
It is quite obvious that about the lower half of the accretion disk is brighter.
This question (or rather, the asnwers) explain that it is caused by Doppler beaming. Since Doppler beaming partly constitutes of Doppler effect, I would expect to see a blueshift on the brighter areas and a redshift on the fainter areas; similarly to what the original rendering of the black hole from the movie &quot;Interstellar&quot; looked like:

(Source)
So why is this not the case for the photo of the M87 black hole?
The picture isn't a &quot;colour&quot; picture - it is monochrome. i.e. It is obtained at a single microwave wavelength of 1.3 mm, and so not at any wavelength you could see (Akiyama et al. 2019).
There isn't therefore any spectral information that would reveal the expected Doppler effect. Any difference of colour in the &quot;false-colour picture&quot; is purely related to the intensity of the emission, not its wavelength.
If one were able to obtain coverage at multiple wavelengths then you might expect a &quot;bluer&quot; (i.e. shorter average wavelength) colour to be associated with the brightest regions.