Change background and font colors of dvipng Equation Images.

[ArielSonique]

To decrease eye strain while reading in dimly lighted environments, I changed the background and text color of Zim by modifying the gtkrc file in the /use/share/themes folder. I chose a dark grey background and light grey text.

However, Zim makes use of a dvipng plugin that generates equation images with a black font on a transparent background. Currently, there is no obvious way to change the background and font color of these equation images. As a result, on a dark grey background (that I chose) the equation images appear as a low contrast black text on a grey background (since they are transparent).

As Jaap suggested in his answer to my initial question, (https://answers.launchpad.net/zim/+question/176239) the lack of contrast in equations could be a problem for people with impaired vision who might use a high contrast color scheme.