1. Actually pastels with a lot of orange is typically an unwanted trait. More orange, the more brown it's going to be as an adult. The more bright yellow, the better.
2. Fires can get that bright yellow cream colored, but not usually as hatchlings. They brighten up with age.
Are you going to breed her or is she just a pet?
Because for breeding purposes, I would rather have a killer fire or a super nice pastel female than a dirty looking firefly. Dirty = dirty babies usually.