WME3D: Limbo of the Lost - sprite color and transparency issue

[joshas]

Please don't ask why, but I've tested Limbo of the Lost on current ScummVM version from git. Compiled a custom build with Wintermute3D engine enabled. With great sorrow I must inform you that game seems to be somewhat working, with one glaring visual issue: some sprites have incorrect colors and visible backgrounds, that supposed to be transparent. Attached screenshot might explain issue more precisely.

Built and tested on Fedora Linux, here are the OpenGL details:

OpenGL version: 4.6 (Compatibility Profile) Mesa 21.3.9
OpenGL maximum texture size: 16384
OpenGL: GL context initialized
OpenGL vendor: AMD
OpenGL renderer: AMD Radeon RX 5600 XT (NAVI10, DRM 3.48.0, 6.0.9-100.fc35.x86_64, LLVM 13.0.0)
OpenGL: version 4.6
OpenGL: GLSL version string: 4.60
OpenGL: GLSL version: 460
OpenGL: Max texture size: 16384
OpenGL: NPOT texture support: 1
OpenGL: Shader support: 1
OpenGL: Multitexture support: 1
OpenGL: FBO support: 1
OpenGL: Multisample FBO support: 1
OpenGL: Multisample max number: 8
OpenGL: Packed pixels support: 1
OpenGL: Packed depth stencil support: 1
OpenGL: Unpack subimage support: 1
OpenGL: OpenGL ES depth 24 support: 0
OpenGL: Texture edge clamping support: 1