How to change the styling of chart js from filled graphs to just lines?
In your widget settings, there's a property 'Filled' on the Appearance tab. Set that to false and you should be good to go!
Paul Ketelaars - Deprecated
You cannot change a bar chart to a line chart through css. Instead, add a new chartJS, and this time choose line chart instead of bar chart
Change the hardcoded color in the java, worked for me.