tweak top threat map colors

findex/src/plot_utils.R

src/assets/images/Climate_and_weather_threat_by_basin.png

src/assets/images/Fishing_pressure_threat_by_basin.png

src/assets/images/Habitat_threat_by_basin.png

src/assets/images/Invasive_species_threat_by_basin.png

src/assets/images/Pollution_threat_by_basin.png

src/assets/images/all_threat_by_basin.png

src/assets/images/threat_by_basin_thumbnail.png