Sorry if this is weirdly worded but when I render something with transparency using Eevee the colours are weirdly desaturated, sometimes fully greyscale, but only when exported and not in the render window
Render window:
Exported PNG:
(With background to show up better on light background)
You cannot export light effects like glow with transparency. Transparency only mixes one image on top of another so it averages colour values, while light glow values need to be added on top of another image. Maybe try rendering emission pass and composite it on top of another image using add operation. Also these effects depend on the image below so they will look different on different images and colour saturation, hue and value may differ depending on the image below - that's how it's supposed to be.
