Actual Result:
Luminosity Contrast Ratio of 'Text' which appears after ''Adaptive cards that is broken because of invalid language' button is 4.0:1.

Note - Same issue repro at -

1. 'Text' which appear after ''Adaptive cards that is broken because of invalid Version' button is 4.0:1.
2. Text 'No renderer for this attachment' appear after activating "Show an attachment of unknown type" button.

Expected Result:
Luminosity Contrast Ratio for 'Heading Text - No renderer for this attachment' should be greater than or equal to 4.5:1.

Repro Steps:

1. Open URL https://microsoft.github.io/BotFramework-WebChat/full-bundle/ in Edge browser.
2. Notice 'Upload File' and 'Send' button icons present in bottom of screen.
3. Type 'Help' in the input control at the bottom of the screen and hit enter (or click on send button).
4. Content will upload, Navigate to any "Adaptive cards that is broken because of invalid language" button by using Tab key and press Enter on it.
5. New data will upload.
6. Open 'Colour Contrast Analyser' and select Foreground & Background color of mentioned elements one by one.
7. Observe that Luminosity Contrast Ratio of text is less then 4.5:1.

User Impact:
Users with low vision or Color blindness will find it difficult to access content with low luminosity contrast ratio.

MAS Reference:
MAS 1.4.3 – Contrast (Minimum) (17)

Test Environment:
OS: Windows 10
OS Build: 17134.345
OS Version: 1803
Browser: Edge
Tool: Color Contrast Analyser

Attachment: