When constructing your anaglyph image, you want to prevent ghosts as much as possible. "Ghosts" are the faintly seen duplicates of the images you want the viewer to see. Ghosts are hard on the eyes and brain of the viewer, and can completely ruin the 3D effect you are trying to achieve.

These examples will show that one way to prevent ghosts is to put detailed images in the background, rather than areas of solid color.

Here's a nickel. It's not in 3D, it's just a picture of a nickel, on a white rectangle. (Depending on your monitor, it might be about actual size, as if the nickel were really stuck to your monitor.)

Now I'm going to try to bring this nickel closer to you. I'm offsetting the images 12 pixels to the left and right, to make the nickel hover about three inches in front of your monitor (assuming, of course, that you are wearing 3D glasses). I'm also making the coin a bit bigger, to enhance the illusion of closeness:

Ouch! It sort of worked, but not very well. The problem is, you can still faintly see just a little of the red image through the red lens, and a little of the blue image through the blue lens. Ideally, your glasses would completely filter out these images; but in the real world, the filtration is less than perfect. The red and blue ghosts cause your brain to fight against seeing the 3D illusion (your brain hates being tricked). You can see the hovering nickel if you work at it, but it's not fun.

Maybe the problem is the white background? Let's try a solid black rectangle instead.

Yuck, that's no better; if anything, it's worse. It turns out that these ghost images will be a problem with any solid background. What are we going to do?

The trick is to put the hovering nickel in front of a busy background, one with lots of detail. The busier, the better:

Wow, now that's 3D! The ghost images have vanished into the baroque details of the background artwork. With no ghosts to bother it, your brain happily gives in to the illusion of depth, and so you can see the hovering nickel without struggling.

The lesson is, your 3D artwork will have fewer ghosts if you put detailed things in the background. Trees are good; so are clouds and starry skies, and tapestries, and canyon walls, and engravings of dragons.