Blend modes

For images in symbol and 3D model representations, as well as single model and 3D Tiles layers, it is possible to select a particular blend mode, which determines how the colour property of the sprite (or model) is combined with its original colour.

The four blend modes that can be selected are the following:

Normal replaces the original colour with the colour property
Multiply darkens the overall image based on the colour property (the impact is stronger on brighter pixels)
Screen brightens the overall image based on the colour property (the impact is stronger on darker pixels)
Overlay applies Multiply on dark pixels and Screen on light pixels

More information on those blend modes can be found here.

Unlike traditional image editing software like Adobe Photoshop, the alpha value of the colour property controls the opacity of the feature, but not the ratio of the two colours used for the blending. Instead, this ratio is controlled by the dedicated per-layer (or per-representation) property feature_color_blend_strength (from 0 which is the unmodified feature colour, to 1 which is the blended colour).