There are 3 research items in my screen shot.
One I am researching, two others which are boosted. One of the boosted has a blue bar (Wheel). Why is it blue?
BOOSTED: Mine a resource
I boosted Bronze working by killing barbarians.
I boosted the Wheel from mining.
Also, I am china and china gets a 60% tech boost on eurekas. I started one turn of bronze working and now the bar is blue same as the wheel.
I decided to research for one turn Masonry but the bar did not go blue.