I would like to know if it is possible to have an entire floorplan (2D) in one colour?
Simple answer is yes, but you need to be more specific about what you want.
So, I am looking to have all the lines and images, such as windows and door openings all in one colour.
Can you show a screenshot of what you have.
Click on a picture to animate:
Easy enough to do that by editing the style. I would probably do that in LayOut if it was my job.