Indentation guides hard to see in darker themes

[kieferrm]

Testing #8232 on a MacBook Pro Retina display with brightness 2 steps below max while using a power adapter. This is my usual setting a regularly lit environments.

In the following themes the indentation guides should be changed to improve their visibility:

• * Abyss
• * High Contrast
• * Monokai

In the following themes the indentation guides are subtle and easy to miss. However, changing those is optional.

• * Dark (and Dark+)

[alexdima]

I am using the invisibles color from the theme, 100% the same as renderWhitespace. @aeschli owns the Dark and Dark+ themes (including the invisibles color):

https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/services/themes/electron-browser/themeService.ts#L385

[aeschli]

@bgashler1 Assigning to the UX team to decide on changes to the default colors.

[sandy081]

Some of the reported themes (Dark, Dark+, High Contrast) are owned by us. Others (Abyss, Monokai) are cloned and packaged along with VS Code. It means indirectly we own them and have to maintain them. So we should provide proper color for indent guides for all these themes.

@bgashler1 Can you please go through all our default packaged themes and come with a nice indentation guides color ?

Note: TM theme setting to use for identation guides is guide.

Also, as mentioned in description, except reported themes others look good to me

• Abyss
• Dark
• Dark+
• HighContrast
• Monokai

[bgashler1]

Reopening until PR is merged in

[sandy081]

Moving this to September milestone, since it is too late to make into August