Question:
How to change background color of plot space?

Answer:
There are two ways to change background color; one is by clicking the "background color" button on the toolbar shown below:


The other is to manually call the subroutine msBackgrounColor() in your code. This procedure takes three real numbers within the range of 0 to 1 specifying the rgb code. For example,
call msBackgroundColor(mf(0.3),mf(0.5),mf(0.8)) will give a blue background.