Saner default for Parenthesis color theme

[jestarray]

https://github.com/user-attachments/assets/ea1b3fc0-4da4-4be6-904f-84e2fa083fa7

The default "Basic Grey" option is a bad default. Defaulting to winter seems more inline with the default color scheme. Beyond that, I didn't even know this was a feature! We should change the default because the coloring helps students see the scope of parens much more easier. Also "Shades of Grey" and "Shades of Blue" don't render as shades at all for me. I'm on racket 8.7 though.