I'm not an astronomer, but I believe the "mottled red" features are distant objects that are redshifted. Note that they're almost all red no matter where you zoom in. That's the evidence that space is expanding in a nutshell.
Distant objects do tend to look redder because of redshift, but the mottled pattern is a bit too regular to all be distant galaxies. It's more likely to be the noise in the data used for the red channel (likely the infrared Ks filter).
