Mid-level clouds depict in an ochre colour in the Dust RGB images.
Ochre contains a higher amount of red combined with a lesser amount of green.
The red colour beam consists of the brightness temperature difference (BTD) IR12.0 - IR10.8. This difference is around zero for mid-level opaque clouds. Given a temperature range from -4°C to +2°C, the red colour contribution is medium to high.
The BTD (IR10.8-IR8.7) is ~(2-4 K) for water clouds and low (around zero) for ice clouds. A mid level cloud is usually a mixed phase cloud so it has a BTD in between. As for the green component a strong gamma correction (with 2.5 gamma) is applied, the green signal becomes medium strong (or a little weaker).
The colder the clouds, the smaller the blue colour contribution. For mid-level clouds, the blue colour contribution is small.
The Dust RGB image below shows ochre mid-level clouds over the Ukraine and Romania.
Dust RGB from 21 August 2015, 12:00 UTC
Explanation of the ochre colour of mid-level clouds in the Dust RGB (see the recipe):
In case of mid-level clouds, red and green colour beams contribute most (with red a bit more than green), while the blue contribution is rather weak.