In Photoshop, I’ve found that setting the layer to Multiply might not always result in the color expected (ie: yellow circle under blue gives you a black center). To make the center green, I put the yellow circle on the bottom layer with the blue circle on the top layer, overlapping the yellow. I set the blue circle layer to color burn. Now that turns the center green, but makes the rest of the blue circle disappear. To get around this, duplicate your blue circle layer (make it just a normal layer) and set it on top of where the blue circle was. While on the yellow circle layer, use the magic wand tool to make a selection around the yellow circle. Change layers to the top blue circle and erase away the blue that is selected to reveal green.