Cloudless land depicts in magenta colours in the Dust RGB in winter time. Due to the cold temperatures, the blue colour beam is very weak. IR12.0 and IR10.8 are slightly different when radiation comes from the earth surface, especially when the land surface is cold. With a positive BTD and a temperature range from -4 to +2 for the red scale, the red colour beam shows strong intensities.
The green colour beam is weak. The magenta colour for land surfaces is a typical winter phenomenon. In summer time, land surfaces depict in blue colours as the blue colour intensity increases with higher temperatures from IR10.8 (see image below).