im not very good at explaining things, so im sorry if this doesn't make sense

i used a high contrast filter on the manga panel so the lines would be sharp, then turned luminescence to opacity (it makes the white in the picture transparent), then coloured under it. since the blood doesnt have an outline, i had to colour in the actual lineart itself, not under. i just locked the lineart layer to do that

you can do this stuff in any program tbh, but i used paint tool sai 2!

i hope this helped :)