The idea is simple. When the background of the script editor is {0,0,0} the text marker (the line thats where your next typed letter goes) should be white.
Otherwise its not visible, and the only way to do this [temporarily] is switch the color to {0-10,0-10,0-10} and the text marker will turn white for a period of time and then turn to black once more, where then you must change the background color property to see it.
lolwat. The text marker isn’t the same color as the text? Bad ROBLOX.
I’ve experienced this also. My drak gray background is a bit hard to work with 
I once bugged the system and my cursor turned to another color or so, maybe that was ‘luck’.
Maybe let us pick our text marker color.