"Do not alter the rainbow pentagram, the spiral, the runes, or the cosmic background. Modify only the green areas of the circle and glow. Replace the green glow with a dark, grayish tone that evokes death and decay. The new color should look metallic gray, smoky, and ominous, blending naturally with the rest of the rainbow gradient. Keep the neon effect, the glowing texture, and the mystical atmosphere intact. Ultra-detailed, high resolution, glowing magical symbol."
Google Nano Banana