Check themes for accessibility before making them available for download

[GeekyPeas]

Discussed in https://github.com/Gogh-Co/Gogh/discussions/60

^{Originally posted by agauniyal March 13, 2017} Some themes like Tomorrow Bright, Monokai and others produce color combinations which are hard/impossible to distinguish things/text on terminals. Try it yourself, choose Tomorrow Bright and open htop which is a widely used system monitor kind of cli application, the portion where cpu usage is shown like -

1  [                               0.0%]

The 0.0% part and similarly other texts won't be visible to you because the background is black and text color is also black there. Several themes make them dark grey on black which is also harder to distinguish. I have tried all themes and there were several which were acting strange with all kinds of cli applications. So I propose to try the themes in atleast these cli applications before releasing them - ranger htop top vim nano.

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In many of the themes the problem is that COLOR_1 is same as/ similar to BACKGROUND_COLOR. I don't see any design philosophy/ policy for this project. I wish to suggest the following design rule, that:

no other colors should be same as/ similar to `BACKGROUND_COLOR`.

This should completely eliminate all readability issue.

Originally posted by @GeekyPeas in https://github.com/Gogh-Co/Gogh/discussions/60#discussioncomment-3497858

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I suggest we should run each color (that is COLOR_1, COLOR_2 etc.) against the BACKGROUND_COLOR via the following method in a stackoverflow answer on "Given a background color, how to get a foreground color that makes it readable on that background color?".

So according to the World Wide Web Consortium’s (W3C) Web Content Accessibility Guidelines 2.0 we must have:

1. contrast ratio of at least 4.5:1 for regular text (12 pt or smaller), and

2. contrast ratio of at least 3.0:1 for large text

Then for every (color, BACKGROUND_COLOR) pair that fails the test, we must replace the color.

Originally posted by @GeekyPeas in https://github.com/Gogh-Co/Gogh/discussions/60#discussioncomment-3498425