When using the ColorMap property for custom powerups, particles appear to react to the the "upper" color as if they're in a colored sector. I've observed this with both rocket trails and particle fountains.
Here's some rocket particles while a grayscale colormap is in effect:
If you set gl_light_particles to false, does it behave more like you'd expect?
I'm not sure what's the purpose of the gl_light_ CVARs. They cause GZDoom to use a very different path to choose a sprite's light level and color whether they're true or false. (Particles are a special type of sprites in GZDoom.)
So the actual problem in the first screenshot was that the particle was colored yellow by the dynamic light attached to the rocket, despite the grayscale colormap?
There aren't any dynamic lights. (They're both disabled and not even loaded.) Those options make no difference to the issue, anyway.
No, the effect more closely resembles Sector_SetColor. In the first shot, the upper color is white, which is normal lighting and makes particles appear unchanged.
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