Oops, I forgot that Lensflare doesn’t generate its own alpha. You’ll need a workaround.
Make your solid containing the flare blue or green. Then apply keylight. When you pick the color sample, choose an area completely outside of the flare.
You may get a slight color shift, in which case you can then apply the Hue/Saturation effect.
Joey Foreman
Editor/Animator
Nowhere Productions, Athens, GA