You'll need a graphics program to make one from scratch.
Paint will do for a simple one.
The better ones use alpha channels, 2 images basicly superimposed to make them "glow".
Change the background color and it will show up as solid white in the game.
But feel free to experiment with this one.
I use Irfanview to edit the pallete to change color, sets size, color depth, etc.
Its free.