I have been asked to make a Jessie cake (from Toy Story) for a birthday party this weekend. My client loves the idea of the cow print on Jessie's chaps. Can any of you suggest how I get the cow print on the white fondant? Paint it on, mix it in? Not sure. Thanks for any suggestions.

i am new at fondant...
i rolled out my white fondant till it was a little thicker than i needed and then added my black and rolled it out to thickness i needed and it looked really good..

i also use "the mat" i found it on youtube...
it works good.... and you can roll fondant thin and still looks good...

You could paint it on, but I would probably do as aubasmif suggested and cut it out in black and 'glue' it on the white.