To reproduce:
1. Create new project
2. Add the attached "rgbtest.dds" file into the Assets folder

Desired outcome: Image colours match the text written on it.
Actual result: On windows, the red channel looks like a rainbow

Note: Adding the same image with different extension names (.bmp, .jpeg, .gif, etc.) results in the desired outcome.

Reproduced with 2018.1.0a4, 2018.1.0a6, 2018.1.0a7 (6b1cfe8b4c1b)
Not reproduced with: 2018.1.0a3

More information and images below.