In the Day Microphysics RGB, large ice particles depicts in red colours.

RGB Color Guide
This guide will come in handy for matching colours in RGB images with cloud type or surface feature. It also works the other way round: you can select a meteorological phenomenon and ask for the colour that shows the phenomenon in a given RGB combination.
The collection contains the standard RGBs created from the MSG/SEVIRI imager and also some RGBs from the VIIRS and AVHRR imagers.
To analyse the colours of an RGB image, an interactive tool can be downloaded from the "All Resources" pull-down menu (RGB Colour Tool).
The descriptions of the recipes of used RGBs can be found under the "User Manual" menu (RGB Recipes).
RGB Color Guide
Snow free, non deserted, vegetated land usually appears greenish or slightly brownish in the Snow RGB. Bare soil may appear bluish.
Sandy desert appears cyan in the Ash RGB images: aqua-cyan when the surface is hot, or greenish cyan (aquamarine) when the surface…
Pure volcanic sulphur dioxide gas plume appears typically (light) green in the Ash RGB images.
Thin, pure volcanic ash cloud appears typically red or magenta in the Ash RGB images.
Mixed volcanic ash and sulphur dioxide gas plumes appear yellow in the Ash RGB images.
Semitransparent ice clouds appear greyish in the HRV Fog RGB images (with cyan tones).
Sea, lakes and rivers (open water surfaces) appears black in the HRV Fog RGB images.