DesignVariables.bgMessageRegular is slightly wrong in dark mode

[chrisbobbe]

I think the current value (HSLColor.fromAHSL(1, 0, 0, 0.11).toColor()) might have been taken from a value that web used in the past? Not sure how we ended up with a wrong value for something that's a named variable in the Figma.

Anyway, the Figma is clear: its bg-message-regular variable in dark mode is #1D1D1D.

Figma screenshot:

Successfully completing this issue requires:

• Changing the dark-mode value from const HSLColor.fromAHSL(1, 0, 0, 0.11).toColor() to const Color(0xff1d1d1d)
• Posting "before" and "after" screenshots in your PR description so we can see the change visually.

[gnprice]

This value didn't come from web; it came from 59f13a9 in #973. (I found that with git log --stat -p -S 'HSLColor.fromAHSL(1, 0, 0, 0.11)'.)

So that was intended to come from the Figma design. I don't know if the value changed later in Figma, or if it was #1d1d1d all along and just got inaccurately converted (and rounded) to fromAHSL(1, 0, 0, 0.11) in preparing that PR.

(This is an example of something we'll get to avoid once we do #831.)