Steve, to be rid of the white halo around your image try the 'matte' option in the save for web screen options and change the color to your webpage background which is black. To change the color of the shadow in Elements the layer must be rasterized first. First thing before you do this is control click the layer in the layers palette (hold down ctrl key and click on layer...this will give you marching ants around your image ) then rasterize ( simplify) then select inverse and go to toolbar>layer>new fill layer ( choose color or gradient )and check 'group with previous'. Pick your new color and play with the blend modes. Sometimes 'overlay' works better depending on the background while other times ' color' gives a better effect. If your layer has already been rasterized and flattened then you can choose to start over

or paint the shadow in manually with painbrush in color mode over the exsisting shadow. There are other ways...always....the more you play the more you'll learn.