The points in the plot above are blue. In vega-lite, we’d just add "color": {"value": "red"} to the encoding section to change this. In vega, however, the keyword color is not recognised. Instead, a distinction is made between fill and stroke. fill corresponds to the area of the point itself; stroke refers to the outline of the point (the circle).
Exercise - Change the colour of the points to red.
Exercise - Change the colour of the point outline to green.
Exercise - In the previous exercise, you’ll see that the outline is very thin. Check the documentation for a symbol at https://vega.github.io/vega/docs/marks/symbol/ to find out how to make this line thicker.
Exercise - Change the shape of the symbol from a circle to a something rectangular. Again: check the documentation.
Exercise - Let’s try to have the colour of each point be dependent on the data itself. Change the data so that each datapoint also has some colour assigned to it (e.g. {"x": 15, "y": 8, "c": "yellow"},) and adjust the encoding to use this colour.