Can't open your project from here but I may still have some useful advice.
Having the redder parts toward the middle is a big part of the problem, I think. The hotter something burns, the whiter it is, so try to blend it from reds and oranges on the outside to yellows and whites in the middle.
I also like to spawn another sprite on top of my explosions that is just a big soft white or white-yellow circle with it's blend mode set to additive and a Fade behavior timed to disappear a little after the explosion does. That way it lights up the surrounding area a little, too.