Using a simple overlay the colors are correct, but when I use a blending mode then the color of the output is either green (for multiply) or pink (for addition)
ffmpeg -i test-video.mp4 -i outro-frames/Outro.%05d.png -filter_complex "scale2ref[scaled][ref];[ref][scaled]blend=all_mode=multiply[m];[m]overlay=x=0:y=0" test-video-outro.mp4
Frame from input PNG sequence
Frame after using multiply blending mode
Thanks to the suggestion from Gyan the color issue is partly resolved by adding
format=gbrp to the filterchain.
Instead of the green tint the animation now starts inversed with a solid black background then flips after a few frames to the correct colors.
The first few frames render incorrectly
Then they switch and become as I’d like them to be