Reproduction steps (without project):
1. Create a new project
2. Add a particle system
3. Add trail module to your created particle system
4. Notice that trails are pink (check "pink trails.png")

Reproduction steps (with project):
1. Open the attached project
2. Open "test" scene
3. Select the "Particle System" game object
4. Notice that trails are pink (check "pink trails.png")

Reproduced on: 5.5.0b2