I have had some experience with Draftsight in the past but W10 refuses to acknowledge it so I'm giving LibreCad a try.
Problems so far -
I am trying to draw an a 3 point arc between 2 points. I that I can bend (at the centre point) to line up with the end points. I simply does not seem to work. I select 3 points off the curve tool and it draws a simply arc without a centre point. What am I doing wrong?
How can I change the colour of a whole drawing so I can superimpose an old drawing over a new?
What you intend, as far as I understand you right, can not be done with an arc command. Try "Fillet" from the "Modify"-tools instead. Watch the tab right of the pen properties tab at the top of the screen above the drawing area. You can set the radius there.
To change the color of a drawing, if the color of the lines are set by layer, it's easiest to change the layer properties. Or mark up the whole drawing by pulling up a window around it and use "Attributes" from "Modify"-tools.