In process of updating my project from 4.13 to 4.15 here is the crazy thing.
The game looks fine in the UE4 window while you’re doing the level design, but once you run it, then it’s black and white? I know it’s generic explanation, but that’s all I have right now.
Do you mean that you dont get any textures on your meshes? (post a pic pls) 
The same exact thing happened to me during on of the game’s cutscene!
I had a Make PostProcessSettings node changing the saturation setting of a specific post process in the level .
When they change the tonemapping for the 4.15 release, some settings were changed so the Make PostProcessSetting node was setting the saturation color to black and white.
If you happen to have a Make PostProcessSetting node, take a look at its settings. 