Maybe it was just gold sparks. Now that I think about it I don't think I've ever personally seen rainbow sparks despite the amount of 5 stars I have. I think they all may have been gold sparks.
Either way...
SRs don't deserves sparks at all and going from silver to gold is evil and almost never results in a servant I want.
Either way...
SRs don't deserves sparks at all and going from silver to gold is evil and almost never results in a servant I want.