Command and Conquer: Red Alert 3 Demo (24710) (the full game probably suffers from the same issue)

Compatibility Report

• Name of the game with compatibility issues: Command and Conquer: Red Alert 3 Demo
• Steam AppID of the game: 24710

System Information

• GPU: Intel HD Graphics 4000
• Driver/LLVM version: 3.0 Mesa 18.1.9
• Kernel version: 4.18.0-2-amd64
• Link to full system information report as Gist: https://gist.github.com/Steap/b4cc3f1bfef34b19b2299f295fdd6a4a
• Proton version: 3.7-8

I confirm:

• that I haven't found an existing compatibility report for this game.
• that I have checked whether there are updates for my system available.

Symptoms

When running the first misson of the tutorial ("Intro to the basics"), the screen is mostly... purple. See the attached screenshot.

This happens when the graphics presets (Settings -> Graphics) are set to "low" or "lowest". With "medium", the game looks perfectly normal.

Reproduction

Run the first mission of the tutorial with "low" or "lowest" graphics presets.

Start by reproducing the first tutorial mission with the low and lowest graphics presets under Proton 3.7-8, then compare the result with the medium preset and the attached screenshot. Done means the game no longer renders mostly purple at the affected presets.