For this Lab, I have follow the tutorial to create multiple layers to classify, select and color data in Mapbox, which is more user freindly than Leaflet and D3 as well as Carto, in my opinion. This method is different than what I have been using in any GIS software portal, as I did not select and create different layer only to edit the color, but just color them automatically by the build-in classification method. However, I guess it makes sense to let us create our own classes of data, as in this case, we manually input the classes but we definitely have more choice to play around the statistics of our data.
The map itself is a population density map of the United States, where the darker color represents higher population density and lighter color represents lower population density. However, for a few states with the highest population density, for example, Rhode Island and New Jersy, the color scheme is not apparent due to, A. The relative small size of the particular state; B. The similarity of with the color of the next class, which we do have a few states either bordering or not really far away from these two states. (Corrected after the submission of the lab).
Reference: Interactive Choropleth Map, Leatlet