After completing each layer in Houdini, compositing and colour grading needs to be done in Nuke. The first thing to do is is to read each layer and then use the Postage node to pass in the data for the next step. For the compositing in Nuke, I used a lot of Roto and Blur nodes to deal with the blurring details around the edges. I also use a lot of Grade nodes to control the colour channel, gane and gamma of each layer.
Take the clouds, for example.
At the same time, we need to do some code usage, such as giving value a declaration and using it to perform some multiplication operations to achieve the desired effect.
In each section we need to adjust the colour channels, gane and gamma via the Grade node to ensure that the required colours are correct and to get a relatively good composite result.