any clue on how to make a divergent gradient color that moves away from the inclined line?

I don't think SVG supports conic-gradient yet, which would be necessary in that case. So we're left with a bit of tinkering https://observablehq.com/@fil/conical-gradient-plot

That is amazing, thanks for the elaborated response! What about non conical, but just "rotated" divergent common gradient?