Corrected color contrast to WCAG 2.0 AA (Accessibility Tweak) - Forms and Alerts

[masterbee]

• Slight modification of contrast on Alerts and Form warnings to pass WCAG 2.0 Colour Contrast AA level
• Included colour fixes as well on bs-callouts class bring them up to passable standard.
• The visual changes on the default theme are very minor since the values were almost passable to start

Note: There is still the primary, warnings, brand, etc variable colour treatment, but these have a larger default theme impact since they touch almost all variations of buttons and progress bars, etc. I am willing to put in a PR for those fixes but there will have to be a some looking through the example to see if the impacts are acceptable.

Keep up the great work TWBS team. Loving version 3!

[masterbee]

@mdo, @cvrebert - just chiming in to see if there are any thoughts on this PR. It is a small tweak to the hex values to bring them up to AA passing levels in WCAG 2 which should helps with the section 508 goal.

[cvrebert]

Aesthetics is entirely @mdo's domain. No comment from me other than don't get your hopes up since some WCAG color-related PRs have been rejected in the past for looking too ugly.

[masterbee]

@cvrebert - Thanks for the chime in, and to help out @mdo's input I have attached the difference via 2 pngs.

Current Contrast (v3.0.1)

WCAG 2.0 AA Contrast Corrected

[adamnbowen]

👍

[archonic]

👍 Awesome sauce.