See that dark green?
It's caused by a tiny mushroom called Blue Elf Cup and is found all across the Midwest in marshy areas. If you keep an eye out while you hike, you might just see a giant fallen tree with tiny blue mushrooms the size of a fingernail turning the entire tree a bright blue/green hue. It's quite the sight to see.
What about all that red?
Well, all that red is called redheart. Along with various purples and yellows, this comes from the heart of the tree, where it has all sorts of hues of red. Similarly Box Elder wood often has flames of red, orange and yellow - some of which can be seen in the piece in the upper left corner of the picture.