how to find out my primer color
Usually primer is white. In some cases the primer might be tinted. This is usually done when changing drastically from light to dark or vise versa but the color of the primer is not intended to be the final color, this is what the paint is for. When it is tinted, it would be tinted to closely match the final color. 

If you want to color match, take a chip of paint to your local paint store and depending on the age, they can usually match it pretty well. I'd advise just using white primer and then getting the final paint color matched properly.