The background looks OK as you have it for your custom version of colors. But for the standard theme, I think there should be no background color, so I would remove the colour from the bottom half, rather than add it to the top. That is more consistent with other pages, I think. But happy to hear from other “colors” theme users if they prefer something different.
I agree the footer is very slightly not wide enough. It has a width set at 99%. If I remove that it defaults to 100%.
For your custom version, I see you have added “width: 100.01%;”. That works, but 100% is all that is needed 🙂
For the standard version, as there is no background it doesn’t really matter as the width isn’t obvious, but I will remove the width setting for next release. It will then default to 100%.