There are only 4 borders to choose from, so using the default colors will not work. Instead, you may only use a value between 1-4.
For example, to change the border color to light blue, do:
Here are the color values:
|Snowy Mint / Light Madang||2|
The colors of borders 2 and 3 are not usable or accessible in any way except as a border color. The use of border colors 1 or 4 along with the appropriate background can create the illusion of a larger graph screen. However, nothing can be draw outside the standard window.