If I understand correctly, you have a line art file (say from Photoshop) that you want to be able to make black or white in InD when you need it to switch...I assume so that you don't have to import different artwork each time (have a blac version and a white one). If you have a .psd file with a transparent background, place the .psd file directly in InD. Then, with the Direct selection tool, choose the graphic (when you first select a frame with the Direct Selection tool, you'll actually be selecting the path that makes up the frame...clicking a second time will select the graphic) and then choose a color from your swatches palette. The .psd can't be flattened, since flattening strips out any transparency that InD will need to show the background through your graphic. Hope that makes sense.