Is the use of colour effective on this map?

Capture

Source: http://datasets.wri.org/dataset/globalpowerplantdatabase

Visual design type: Map

Name of tool: Tableau

Country : World Map excluding Antarctica

Year: NA

Visual mappings:

  • X/Y = Longitude/Latitude
  • Point location = Average country latitude/longitude
  • Point size = sum of capacity in given country
  • Point colour = GDP

Question:
I am attempting to plot an overview of the way GDP levels affect national energy capacity. I am wondering if the use of colour for the points is effective, or should Upper middle and Upper be changed to more easily distinguish them?