Use different purple

[XAMPPRocky]

This updates the colour scheme based on talking with @pietroalbini to use a purple that is more deep blue.

• Try It Out — https://www-try.rust-lang.org
• Staging — https://www-staging.rust-lang.org
• Production — https://www.rust-lang.org

New / Production

New / Master

[pietroalbini]

I'd slightly prefer a saturation of 30% / 35%, but this looks way better to me! @Manishearth what do you think?

[XAMPPRocky]

Here's a screenshot of 30%, personally I don't like it as it looks too gray compared to the new purple.

New / 30% Saturation

[pietroalbini]

The color introduced in the PR is starting to grow on me! Let's wait for @Manishearth's approval and then we can merge this.

By the way, I chatted with Erin and it turns out there was a miscommunication, the color with 30% saturation I was proposing is #312a4f.

[Manishearth]

Yeah, this looks way better to me as well (and my understanding is that in the poll about colors people liked the new green but not the new-now-old purple)