Highcharts is a plugin that Knack has bundled in to their product: https://www.highcharts.com/
I've tried to manipulate in the past with jquery with frustrating results.
Altering highcharts graphics can be a real pain in Knack because they are rendered separately from the Knack DOM. You can't 'wait' for them to render before calling a function.
I'm working on a solution to retrieve Knack models and build my own charts that I have more control over. I will post when I have something worth posting.
In the meantime........................
I stumbled on this code a previous developer had added to a site I've worked on. Not sure if this is helpful to you but it appears he was specifying the order of colors in highcharts.
colors: ['red', '#c68c53', 'yellow', 'Green', 'grey', 'blue', 'orange', 'violet', 'light green', 'light grey', 'black', 'dark green', 'dark grey', 'pink', 'magenta', 'fuchsia']
more on setting options here: https://www.highcharts.com/docs/getting-started/how-to-set-options