Fantastic and very useful brushes! However, to make a brush pipe colour changable, you need to make sure it is in greyscale mode. Then like .gbr brushes the black will be counted as full opacity colour and the white will be counted as transparent - everything in between will be a combination thereof.
Hi Banana! Yes absolutely right. In greyscale mode what apprears as white in a *.gih brushpipe is transparent when you use it. Black turns out as whatever colour you choose when you use it. The shades of grey become the shades of the colour you choose when you use it. However, when you actually make the brush it looks like it will just be a greyscale brush, but when you save it as *.gih and use it, it will turn out differently.
Hopefully that's a bit more clear. You can also download my "Sparkliness" brushes, there are a few colour changeable examples.
Anyway, your brushes are fantastic - keep up the good work!