A tip: If you care to install software, install
paint.net so you can work with transparancy.
Start with a transparent screen, select a color manually (so you can enter its settings), select the color black (or any color for that matter that fits your needs, but black is best in this case), on the bottom right, select a
Transparancy - Alpha of 80 or 90. (look what you like best) and fill the entire screen with this. Then save as png.
The effect that you'll get now, is that Juni will be barely visible as if the lights were out, but there still comes really little light from somewhere. (you almost always can see in a dark room even if its almost barely. This is the effect that you'll create. Things will be hard to see, especially if you choose 90, but they are visible. If you have a bright background, it will be really dark, but it will make seeing juni more easy.