How do I paint a turtle shell onto rocks for a garden display?

Hi. I'm making a garden display with rocks. I've collected & brought home different sizes of rocks. One large oval shaped one for the shell. 2 medium size rocks that are oblong in shape, but rounded at both ends,for the head & tail plus another 4 other rocks which are smaller for the legs. I have 7 of these put together. Just need to paint. Was looking at mud turtles, or painted turtles &, snapping turtles. Looked on-line, I got some pictures of different kinds of turtles. Also seen someone else did. Which they have done a couple of turtles which have a white body & blue striped or checkers print for the shell. Also blue head, tail & feet. It looked gorgeous. They will be in front of the sewer waste tank in the front yard. Behind this is my flower bed, which I painted a medium blue around & on the rocks I used for the border. Look terrific this way. With the many different flower s & color in it. Nothing taller than a latrius, dwarf phlox, forget me knots, & pansies. so looking for paint ideas to do these. Possible with green paint, black paint & yellow paint colors. These are the colours of mud turtles or painted turtle or the snapping turtle. Can you help please. For the borders of rocks I painted used Tremclad medium blue color. Paint needs to be water proof or weather proof. These are staying outside. Need to know the best paint to go with which can get the best paint for the job. Looked at spray paint, but realised that you can use it for the bottom coat of paint for the body of shell. But then you couldn't due the stripes on the shell. Which you can't do for spray bottle.