What are some of the strings that brighten the sound of
We don't know what your violin is, so if it isn't optimally set up by a luthier then it could be a fruitless (and expensive) business finding strings to brighten it. Trouble is, violins are individuals, and a string set on one may very well not work as you want on another.
I found that Pirastro Flexocor-Permanent strings brightened the sound of my more mellow-toned violin. These are steel-core strings.
I remember once buying Thomastik Alphayues when I was out in the boonies and the only music store nearby was a guitar shop.
I took it to a luthie in London Ontario in November /2017. He checked out the whole violin and suggested I get a new set of Pirastro Tonica which I have used for many years so he put a set on. I have tried Dominants too and prefer the Tonicas
You could try Evah Pirazzi Greens. My violin loves dark strings, so the Pirazzis sound terrible on it. They're very bright for my tastes. You can email Pirastro and ask for a trial set of something they recommend. Just make sure you tell them your violin's tonal tendencies and what you're looking for. Be as specific as possible.
Assuming that the Tonicas don't feel bright enough, I'd try Warchal Brilliant Vintage. They're reasonably priced, especially given their longevity.
+1 For Lydia's suggestion for Warchal Brilliant Vintage.
Carlos and Lydia,
Thank all of you for your suggestions. It is a great help
Spirocore and Tonica