I selected the background of the image with the magic wand tool (fig 1). Ctrl+command+i to select the inverse. I selected the yellow color from the robot using the eyedropper tool. I created a new layer and filled the selected area with yellow (figs 2 and 3). Then I deleted the original image (background layer). I used the erase tool to remove unwanted pieces from the remaining yellow layer. I chose to remove the antenna and wheels from the yellow layer since there will not be any yellow on these parts in the final image (fig 4).