Trouble with overlaying images in CSS

I'm trying to overlay 5 images that are all the same size, namely 614 w x 814 h. Because parts of each image are transparent, together they make one whole picture. I can't use my original images to show you because they've got personal data on them. Instead I used color blocks to show you an example I've made.

Fiddle

I'm trying to center all of the images in the center of the screen, and it's crucial that they remain there, no matter how far the browser is zoomed in, or if the window is resized. To do that, I use this code per image:

#blue{
margin-top: 10%; 
padding-left: 0;
padding-right: 0;
margin-left: auto;
margin-right: auto;
display: block;
width: 33%;
height: 100%;
}

My question is: How do I center these 5 images in the middle of the screen, having all them overlay eachother like so; blue < green < purple < yellow < red. And still keep them positioned so that there's no space between each image, so that they may form one block of five different colors?

Is there an easier, more accurate way of doing this than what I've shown you in the fiddle?