@zhuixingmomo Hello! I use Clip Studio Paint. The method I use is the following: 1- Apply a "Remove JPEG Noise" filter. 2- Create folders by sections (accessories, hair, eyes/mouth, clothes, body (including subfolders like nipples, anus, vagina, etc). Each folder must contain an image of the work. 3- Inside each folder we create a correction layer "Gradient Map". We are testing what colors we like for the gray scale (play a little with the program, you will realize when you start to modify things in this layer). 4- Once the color has been chosen, apply a clipping mask and delimit the selected parts.
That's all. You have to do this with each section of the drawing. I recommend having a drawing tablet, the cheapest one, to quickly delimit sections. You can also build a color palette. You can capture images from hentai videos and start taking colors of skins, hair, eyes, clothes, fluids, etc... If you don't want to do this process... Well, you can play as you like.
If you have questions you can send private messages and we'll talk a little. In case you have Twitter you can look for me as @SaintBrian20, so the conversation will be more comfortable and I can share images of the process with you.