The thumbnail of RasterMap is a part of the "VectorAnalysisMaps" representation. It is located in the field -> rasterAnalysisMaps -> geoMaps attribute and the geoMap contains a thumbnail.
Color schema is applied via the env attribute: env=v1:-0.0689999982714653%3Bv2:0.12600000202655792%3Bv3:0.24799999594688416%3Bv4:0.31299999356269836%3Bv5:0.4269999861717224, where %3B is ; symbol.