I'm surprised this image scored so low in the challenge. Looking at your camera you've done very well for a .3MP camera... Although no-one knows this during voting unfortunately.
Personally I thought it was fairly yellow... Perhaps you could have fiddled in photoshop (or similar) to increase the amount of yellow.
Finally, did you take this shop from a tripod or handheld? If you say handheld then you did really well to get it this sharp even - I tried fireworks once and made a terrible mess than to the long exposure and camera shake.
This is a nice abstract photo. However, I would prefer that the sparks not be over-exposed. I know these types of photos are very challenging, and unfortunately, I have no suggestions for technically improving this one.
This is a difficult shot to take as the camera has to focus quickly on the subject in a very small amount of time and it is not easy taking photos of skyrockets, I tried it often. You didn't quite get the focus in unfortunately. The idea is original for the "yellow" challenge and had it worked properly you would have gotten a top score.