Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 388.31
Broken: version: 2.81 (sub 10), branch: master, commit date: 2019-09-09 20:20, hash: rB3e81c1c1d5fd
Short description of error
color mix node in eevee set to darken wont result in correct output, when fac is lower than 1
Exact steps for others to reproduce the error
add a colormix to the surface shader's color (for example). set the mix mode to darken. choose white as color1 and a dark color as color2. gradually change the factor value. you see a different behaviour in cycles, where the white output at factor 0 darkens when raising the factor to 1.
in eevee at factor 1 its correct, but it only turns black, as you lower the factor to 0. It should turn white, like in cycles.