Convert an image to a single level colour with imagemagick

Use this:

convert input-file.jpg  -colorspace Gray +level-colors ,#db5131 output-file.jpg

To convert an image like this:

To an image like this:

Replace the hex value with whatever colour you want, obvs.

Batch convert all the JPG files in a folder like this:

for i in *.jpg; do convert $i -colorspace Gray +level-colors ,#db5131 $i; done