Please describe the problem:
Gaussian Blur produces a Dark Border when used with any color.

Steps to reproduce:
1. Open a new Image with white Background
2. Make a new Transparent Layer
3. Draw a Line, Dot etc. with a bright color, e.g. Red
4. Use Gaussian Blur, any setting should work, use one which makes a Blur you can see


Actual results:
The Border isn't just blury it is dark and slightly black.

Expected results:
Border Color should have the same Tone like the Dot/Line etc.
Like it did in older Versions of Gimp.

Does this happen every time?
Yes

Other information:
Older Versions of Gimp have a working Gaussian Blur (e.g. GIMP 2.2.10) if you encounter the problem you could just use the gblur file of this in GIMP 2.2.12 to workaround the problem.