ColorifyAI (https://colorifyai.art) generates coloring drawings from an instruction or image.

Several styles and formats offered.
Export png and pdf, share url.

Free, without an account and unlimited.

Tests from Wikimedia Commons images: https://commons.wikimedia.org/wiki/File:Fort_de_Joux_02.jpg and https://commons.wikimedia.org/wiki/File:Soba-Noodles-Deliveryman-Tokyo-1935.png?uselang=fr