Better defaults for light mode

[edmcman]

As a new user, I could not figure out why light mode did not seem to work. It appears that the default colors, which include alpha, are the same for both modes. In light mode, this made the lines almost invisible.

[Odrin]

I can propose my color palette:

"indentRainbow.colors": [
    "rgba(200, 200, 200, 0.4)",
    "rgba(114, 168, 223, 0.4)",
    "rgba(139, 190, 138, 0.4)",
    "rgba(209, 154, 102, 0.4)",
    "rgba(184, 128, 185, 0.4)",
    "rgba(214, 143, 143, 0.4)",
    "rgba(179, 173, 119, 0.4)",
    "rgba(105, 176, 174, 0.4)",
    "rgba(204, 180, 134, 0.4)",
    "rgba(154, 148, 223, 0.4)",
]