BUR #4448 has been approved by @evazion.
create alias solid_white_thumbnail -> solid_color_thumbnail
create alias solid_black_thumbnail -> solid_color_thumbnail
These tags are useful to detect images that cannot be matched by IQDB and for other automated scans or machine learning based on thumbnail processing, however we don't need to have a variant for every color.
I'm planning to eventually populate it when I finish catching up on my IQDB misses scan.