I weren't able to solve my issue using your .set syntax, so I went another way and used jQuery to set the CSS value directly.
$(element).css('background', ('linear-gradient(to top, transparent 48%,' + lineColor.bg + ' 1%, transparent 49%)'));
Here's a forked working example :
See the Pen mPwBEW by francoish (@francoish) on CodePen
By the way, if you have any way to draw a line from the left to the right to a set position using Greensock, I would be absolutely delighted. I want to connect some aligned dots with a line coming from the left to the right through them.
