On Sun, 4 Oct 2020, Ioannis A. Venetis wrote:
At least in plain time series graphs the gretl plot control had a
"palette" tab where we could change/set the first 8 (i think) series
colours. It is no longer available in gretl2020d.
That option has been superseded by the "Graph theme" control under
/Tools/Preferences/General. However, you can still set plot-specific
line colors in the plot editor, under the Lines tab.
Allin