I see this was added a while back, so construction site's percentage color will vary between red, yellow and dark green. (Not 100% sure about the green color, but it might be a compromise to allow it to stand out on all terrains.)
However, wouldn't it be nice to reuse these colors for the production status. Afterall, you usually have more buildings than construction sites, so that's what you will mainly be interested in.
I see this was added a while back, so construction site's percentage color will vary between red, yellow and dark green. (Not 100% sure about the green color, but it might be a compromise to allow it to stand out on all terrains.)
However, wouldn't it be nice to reuse these colors for the production status. Afterall, you usually have more buildings than construction sites, so that's what you will mainly be interested in.