I want to create a .png file which is just a solid color.
This must be easy to do using ImageMagick but I can't figure out the problem:
C:\tmp>convert -size 8x16 -stroke black -fill black -draw "rectangle 0,0,8,16" black.png
Magick: missing an image filename `black.png' @ error/convert.c/ConvertImageComm
and/3016.
Obviously there can be more options, like borders and etc, but if you just want an image of width x height of a given hex color, it's pretty straight forward.
Here's all it takes to make an 100x100 image of a solid dark red:
convert -size 100x100 xc:#990000 whatever.png