For keeping the nearest clouds you should use the settings the other way around.
The way you've set up your distance shader's settings is as follows:
0 metres from camera = black
500 metres from camera = white
Result is a gradient from black to white from 0 to 500 metres, the first 500 metres from the camera the cloud coverage will gradually increase. Obviously, the cloud you want to keep, is further away than 500 metres from the camera, since it is still shown using these settings.
If you reverse these numbers the coverage of clouds will be reversed.
The result will be that all of your clouds are gone. (remember that with your settings all the clouds are visible, also the one of interest) So you will have to increase the near color distance. Increasing this will "push" the black color further away from the camera.
If you increase the far distance as well the gradient becomes less smooth.
So for example:"
Far distance = 400m
Near distance = 500m
The result is: from 0 to 400m from camera the color is opaque white. Then from 400 to 500m from camera the white will gradually
change to black. From 0 - "infinite" metres from the camera the color will be opaque black.
You can always start a new tgd, set the camera close to the ground and use a distance shader as blendshader for a white surface layer. You can then play with the settings to see how they work.
Hope this all helps.
Martin
