I worked this out for radiation areas, but I'm stumped on temperature.  When an entity spawns, how might I determine whether it's in a cold area or not?

Nevermind, finally found it in BiomeChat plugin:

        string LetsStringThisBiome(Vector3 Position)
        {
// arid
           if (TerrainMeta.BiomeMap.GetBiome(Position, 1) > 0.5f )
           {
                if (debug) Puts($"arid > 0.5");
                if (color_use) return $"<color={color_arid}>{name_arid} </color>";
                else return $"{name_arid} ";
           }
// temperate
           if (TerrainMeta.BiomeMap.GetBiome(Position, 2) > 0.5f )
           {
                if (debug) Puts($"temperate > 0.5");
                if (color_use) return $"<color={color_temperate}>{name_temperate} </color>";
                else return $"{name_temperate} ";
           }
//tundra
           if (TerrainMeta.BiomeMap.GetBiome(Position, 4) > 0.5f )
           {
                if (debug) Puts($"tundra > 0.5");
                if (color_use) return $"<color={color_tundra}>{name_tundra} </color>";
                else return $"{name_tundra} ";
           }           
//arctic
           if (TerrainMeta.BiomeMap.GetBiome(Position, 8) > 0.5f )
           {
                if (debug) Puts($"arctic > 0.5");
                if (color_use) return $"<color={color_arctic}>{name_arctic} </color>";
                else return $"{name_arctic} ";
           }
           return "NOBIOME";
        }​