While I do like the different versions, what I can say about the yellow is I wished she had some bright red to help compliment her symbols. The yellow is very pretty (and yes, the blaze too!), but looking at her next to the others, she seems a little washed out. Red came to mind to represent fire, and lead to the fireworks symbol.
The original, with her pink, just looks weird. I always thought so, since pink and orange have never been a favorite color scheme of mine.
That leaves the other options...3 and 4 colors. It is hard to say which I would say I have a preference for, as the colors are somewhat hidden by their nicely brushed appearance. It's obvious these girls were primping for their photo shoot! The 3 color scheme matches her symbols very nicely, although with the 4th color, it does give a little more contrast and brightens up her overall appearance. Maybe we are just getting to the point of liking matchy matchy for hair and symbols, so those options are most appealing.
Nice job though! Sparkleworks was always one of my least favorite ponies, and at least with the different hair options, she seems to have a little more unique personality than she used to.