Color Selective Blur [colorblur.exe]
Author: Tibor Bamhor [aka: tiborb95]
In menu: Filters → Blur → Color Selective Blur
Source & homepage here.
"... Gimp plugin that selectively blurs the color information (both hue and saturation) and optionally brightness in image.
There are about three basic scenarios / reasons to use this: * saturating poorly saturated images * denoising noisy images * creating cartoon-like images.
The plugin blurs selectively, and a side effect is that it "sharpens" transitions between two colors.
The plugin have three basic outputs - blur color only, blur also brightness (~cartoon mode, with two variants) and creation of lines..."
Compilation by Samj here.
Same plugin version compiled in two different orientations:
1. Orientation VERTICAL: