If you open a new file and change the colors for the first graph ( in the Style settings), the remaining graphs you add in that file will use those modified colors.
If you already have multiple graphs, you can also use the gear menu and select “Set same style for every graph” to transfer the style settings between graphs. You can also copy and paste the Style settings from one graph to another, and between files.
1 – Right click on the style settings with the colors you want.
2 – Click on the thumbnail of the graph you want to apply them to.
3 – Use Command-V to paste the settings.
This transfers all the settings not just the colors.
It sounds like what you might be interested in is an overall preferences panel for the color presets? Or maybe a way to copy just the color menu from one graph to another?