All colours used in each example have been tested against the WCAG Standards, with most coming out as AAA. There’s going to be small colour shifts inside of the images when they’re converted to a .png to be displayed in the Article.
The example used is yes, like you say, for a very small form, so I would be inclined to do things a little differently if the form was much larger.
Agree on the Labels though. Note to self on that schoolboy error ;)