Version: 2.73 (but also 2.74 rc2) linux 64
How to reproduce:
- Open the attached file and inspect the simple blue cube material and freestyle settings.
- Notice that the line color and emission color values are identical.
- Render the scene and notice that the emission shader emits exactly the same color as set in the properties, but the freestyle line is much darker than expected.
- Try the same thing in BI and notice that the freestyle color space is not affected in this way when rendered with BI.
If this is an intentional aspect of Freestyle in Cycles, I cannot figure out why.