I would leave it alone and enjoy it. I for one wouldn't change or tinker with an important part of my tank just in hopes of getting color on a coral. Color comes more from stability and the right tank environment. Once settled in for a while it will probably get pink tips again. Mariculture Millie's change color a lot. Normally ones that look almost all yellow with orange tips turn out to be green with a little color in the tips. Most of them change colors and or shades dramatically and are hard to keep the original color the sun has given them. Zeo tanks are the only tanks I have seen keep neon pastel colors on corals, and even then it may not be the same color they were when they were in the ocean being cultured. The redish colored Millie's do like high par though.