PIL and font colours.

[Johny]

 I use PIL to write some text to a picture.The text must  be seen wery
clearly.
I write the text to different pictures but to the same position. As
pictures maybe  different, colour, in the position where I write the
text, is also different.
Is there a way how to set the font colour so that it will be seen very
clearly in the picture?
For example, if the picture is bright ( for example yellow), the font
colour should be dark( e.g. black) and vice versa.
Can anyone help?
Thanks
L.