How to assign different colour for various parameters while creating a matrix plot using Vega-lite? How to fill the dots with those colours that I assign? All the dots appear with the same colour when I plotted, the image is given below

How to assign different colour for various parameters while creating a matrix plot using Vega-lite? How to fill the dots with those colours that I assign? All the dots appear with the same colour when I plotted, the image is given below. Please help me with the code