The color of lightning is usually a reflection of the particular gases being ionized/the refraction of the light through the atmosphere. In the comics it's usually just artistic choice.
I was really hoping it had something to do with her power signature but you're absolutely right about it being an artistic choice.
ALL HAIL THE HADARI YAO, THE OMEGA'S OMEGA, BEYOND OMEGA, THE VOICE OF SOL!!!! NOW AGAIN THE ONE TRUE AND ONLY GODDESS OF THE X-MEN AS CLAREMONT INTENDED!!!!!