Thanks so far. I managed to include vertexColors etc., so that my lines are now all BLUE (see line 206 of the sourcecode in my link on the previous post with …v1.8.html instead of v1.7… at the end - sorry I am making this so complicated, but my post got flagged/blocked twice because of posting links…). Next I tried to change line color on the fly, so I made a quick&dirty setup by adding lineNumber in the controls, and by changing this, I can see that the colors array changes (see line 168 of the sourcecode and the lines before / quick explanation: there are 1394 lines with 5 vertices each). Then I tried different ways of updating the canvas as explained in threejs-docs: #manual/en/introduction/How-to-update-things under “BufferGeometry” but I cant get it to work… Any hint?