I've seen many splatter brushes for Gimp all over the internet. I wanted to make some, but I could not find a tutorial on how to make them. Because of that I've figured out my own way to make a muddy splatter brush in Gimp and I'll let you in on the secret.


1) Open up a New File in Gimp 450 x 450
2) Before clicking OK go to Advanced Options > Fill With > Transparency
3) Click OK
4) Choose Sparks as you brush and create something similar to Attachment 1 (Anything random will work though)
5) Now go to Layers > Colors > Colorize
6) Hue 0 | Saturation 0 | Lightness -100 |
7) You should now have something similar to Attachment 2
8 ) File > Save As
9) Name your brush "Splatter Brush.gbr"
10) The Save as Brush box should pop-up
11) Leave the Spacing as default (10) and change the Description to "Splatter Brush"
12) Install it and make some art!

Attachment 3 is an image made with splatter brushes I made myself.
 

Hey Yuiko,- Welcome to the board   I don't really know about Gimp brushes, but for other photo shop software, brushes are saved in black with a translucent background. When you use the brushes, just pick the colour/ gradient  you want to use use, and your brush will be that colour/gradient .  So no need to save brushes in various colours. Hope this helps