To reproduce:
1. Open attached project "HairTest.zip"
2. Open "test.unity" scene
3. Enter play mode
4. Observe as a new hair model appears and it's white, even though it has the same shader as the brown hair

Expected result: both hair have a shader assigned and don't look white
Actual result: hair model with material which is downloaded through a script looks white

Reproduced on:
2017.2.3p1 2017.3.2f1 2017.4.6f1 2018.1.5f1

Notes:
2018.2.0b9 2018.3.0a2 - the hair model doesn't appear