lllyasviel
commented
7 years ago 
In short, you can upload a sketch and a reference, and just click colorize.
What is important is that your reference image will become a color picker once it is uploaded. You can select any color via clicking your reference image and give hint to the AI via clicking your sketch, just like paintschainer.
Just click the reference and then make some pointed hints on your sketch.
You can give the AI many hints like this.
But keep in mind that the AI is very sensitive to your hints. In most cases, a single and small point is fine. You do not need to so much some messy hints to cover sketch blocks. Small and pointed hints are recommended.
These 4 toggles are very important.
In some cases, shifting these toggles will make a big improvement in colorization.
So we recommend you try all of these V1, V2, V3, V4 for your sketches.
You can try this toggle to denoise the result.
Good luck and have fun.
English Version is below to this chinese version
简单的说就是先上传一张参考图，再上传一张线稿，再点击上色就好了。
需要注意的是，在你上传参考图之后，你的参考图就会变成一个调色板，可以点击，然后就可以用选好的颜色在线稿上面画点。
具体用法是点击参考图上的颜色，然后点击线稿上面对应的点，然后就可以给AI颜色参考。
通过这样的点击，就可以给AI各种提示。
需要注意的是，AI对于这些点十分敏感，只需要轻轻的点击一个很小的点就能起到很大的效果，所以建议只点击几次鼠标。（上面那个图片中就是一个小的点，一般点这么小一个点就够了）
这四个选项非常重要，用法是先换选项卡再点击上色。
有的时候切换选项会产生巨大的改变。比如这样：
总之建议对于每张线稿都试试所有的V1,V2,V3,V4。
应该会有所改善。