Check themes for accessibility before making them available for download

[agauniyal]

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.

[Mgldvd]

your right
pull request are wellcome :)

[bohlender]

Does this really have to be performed manually? I think it should suffice to analyse once which colours are used for adjoint elements of the mentioned CLI applications, e.g. htop uses COLOR_1 for the percentage values in the CPU-& RAM-usage bars on a BACKGROUND_COLOR background.

Having identified all such pairs of colours, we can assess a theme's accessibility/legibility by calculating the difference in terms of hue/brightness for each pair. A small difference will indicate that the colours are similar but used by some CLI application for neighbouring elements.

It's just an idea in case someone wants to tackle this issue using a semi-automated approach.

[polemon]

Well, you could invert the install process, as in by selecting the theme, it'd only change the current settings and then ask whether that theme should be kept or not. At this point it'd be the easiest to do it for each terminal-type individually, as not all terminals support changing current settings immediately.

[GeekyPeas]

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.

[GeekyPeas]

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.