changing the color from black to blue on an image. Help on imagecolorset.

Hi there, I would like to change the color on a png file from black to blue. This png file is transparent and contains only a spot which is black. It is needed to stay transparent because I am gonna merge it later on with a jpeg. I tryed imagecolorset but anyhow I do not understand the syntax. Here is my try: # set home color $farbe_b = imagecolorallocate($country_image,0,0,0); // create index for the black color imagecolorset($country_image,$farbe_b,51,51,204); // darker blue Can anybody help on this. Thanx in advance, Andy