I was thinking that you want to change a lot of pushpins at the same time.
To make a hide picture, just open any picture you have with Paint Editor.
Fill all with the same color. and the job is done.
Pixel(0,0) means that the color you have in pixel(0,0) is the hided color.
If your Pushpin is a blue car with a red forecolor, the pixel(0,0) has to be red if you want to see just the blue car without any red forecolor.
The interest of that, is that you can see the red forecolor if you put a green color in the pixel(0,0).
I hope it's clear for you.
( Reading all your posts, in the purpose to help you, I still don't understand very well what you are doing. Are you changing manually pushpins one by one? )