Semitransparent ice clouds depict in green colours in the Day Microphysics RGB images.
Semitransparent clouds, as the name indicates, do not reflect short wave radiation from the sun. They are optically transparent and therefore not visible in the VIS0.8 channel. No contribution from the red colour beam.
Small ice crystals reflect much of the incoming short wave solar radiation at 3.9 micrometer. A strong green signal results from this cloud property.
Semitransparent clouds are very cold, hence no contribution from the IR10.8 channel.
The Day Microphysics RGB below shows thin cirrus clouds which develop at the coastal mountains and spread over the Mediterranean Sea.
Day Microphysics RGB from 7 February 2016, 12:00 UTC
Explanation of the green colour of semitransparent ice clouds in the Day Microphysics RGB (see the recipe):
Only the green colour beam contributes substantially because small ice crystalls strongly reflect short wave solar radiation at 3.9 micrometer.