Why doesn't the build time/cost change when I change ministers or research a new tech?
Any modifier that affects build time and IC cost, such as a minister change, an assembly-line tech, or event, has no effect on what is already in the build queue. New production orders created after the change will take into account any sort of time/cost modifiers. As of the 1.2 patch in the HoI2:Doomsday expansion, build times and costs do change.
Why do I have a red number in my factory information display?
A red number indicates you have some wasted industrial capacity.