I’m experimenting with cel-shading, and to get manual control over the color I’m adjusting the emissive color. However, the resulting color is washed out, and it’s very noticeable on certain colors. This occurs on both “Unlit” and “Default Lit” shading model settings.
The expected color can be see when the viewport is “Unlit”, but it is washed out in “Lit”. The effect can be seen in the material editor viewport (I also tried setting the 4vector alpha to 1.0, it didn’t have any effect):
The tonemapping is on by default. That third link is about the changes made to the default tonemapper in 4.15, so that could be your issue. The comments there talk about the issue and how to adjust it or get better results with it. I’ve disabled it completely in mine for now so I haven’t experimented with any of the modifications.