You will need a combination for this. The glow bit needs to be additive, and the solid bit, well, needs to be solid.
Split it up into two sprites, one solid one for the center bit, and then another glowy bit. The glow needs to be additive, the center bit, just normal blend vertex color will do. In your scene, place the glowy one BEHIND the the solid one. Should be a close enough effect now, and if its not bright enough, stack up 2 glowy ones...