In GMAT R2016a, certain actions can trigger the GUI to enter/leave "Advanced Mode", where the mission and resource trees are grayed-out, and only the script is edited. In the process of entering/leaving Advanced Mode, the trees' background color is changed to indicate whether they are active. The colors, as presently used, assume a "light" GUI theme, and assume that the default background color is white. This causes problems in dark GUI themes, which have white fonts on a dark background. The result is that the mission/resource trees are unreadable after loading a script file (which causes a toggle of Advanced Mode).
Attached is a small patch to pass wxNullColour, instead of WHITE, to SetBackgroundColour in these cases. This causes the backgrounds on the mission/resource trees to be properly reset in dark GUI themes.