Better default colors for plots

[FedericoStra]

I accidentally opened this issue bheisler/criterion.rs#547 on criterion.rs instead of here. #11 is also another similar issue.

The problem seems to be that https://github.com/bheisler/cargo-criterion/blob/main/src/config.rs#L25-L34 defines the colors as

static COMPARISON_COLORS: [Color; NUM_COLORS] = [
    Color { r: 8, g: 34, b: 34 },
    Color { r: 6, g: 139, b: 87 },
    Color { r: 0, g: 139, b: 139 },
    Color { r: 5, g: 215, b: 0 },
    Color { r: 0, g: 0, b: 139 },
    Color { r: 0, g: 20, b: 60 },
    Color { r: 9, g: 0, b: 139 },
    Color { r: 0, g: 255, b: 127 },
];

instead of https://github.com/bheisler/criterion.rs/blob/master/src/plot/plotters_backend/summary.rs#L12-L21

static COMPARISON_COLORS: [RGBColor; NUM_COLORS] = [
    RGBColor(178, 34, 34),
    RGBColor(46, 139, 87),
    RGBColor(0, 139, 139),
    RGBColor(255, 215, 0),
    RGBColor(0, 0, 139),
    RGBColor(220, 20, 60),
    RGBColor(139, 0, 139),
    RGBColor(0, 255, 127),
];

Probably in the copy-paste the red channel got somehow reduced modulo 10.