granite
Blue and gray together make a color that is considered hazel. Blue is considered blue not hazel. Gray is considered gray but sometimes is called hazel.
You can buy them, they are usually made of foam. You can make you own very easily with either foam or cardboard as well. Spray paint them grey and write funny or scary rips on the tombstones.
Gray and purple mixed together will make a less saturated shade of purple - that just means it is closer to gray than purple.
black and white make gray
A lighter gray.
To make gray, you mix black and white.
gray
Dark gray.
Tombstones can be made from a variety or materials. In early America they were made from slate. Slate's tendency to deteriorate, however, led over time to a shift in choice towards Granite, which is a much more resilient material. Marble and sandstone are both also used.
gray and orange will make an ugly muddy color
The colors teal and purple make a blueish gray color.
White and gray together will make a lighter gray. Red and green will make a brown. Light gray and brown together will make a neutral color, also called greige or a greyed brown.