please help!!

i am trying to make brushes for gimp
i know how to make them but i cant make them so they change to the colour chosen on the colour pallete for example i made a brush which was black in the shape of a star and saved it. but when i use it can only be black i cant change it to be a different colour. i hope you understand what i'm saying.

PLEASE IF ANYONE CAN HELP PLEASE WRITE BACK ASAP!!!!!!

THANK YOU
XXX