MEDIUM: stats: compute the color code only in the HTML form

MEDIUM: stats: compute the color code only in the HTML form

The color code requires a complex logic, and we use it only in the
HTML part. So let's compute it there based on the server state, its
health and its weight. The thing is tricky but OK. There's a 1-to-1
mapping of down servers, but not of up servers, hence the need for
the weight and health.