Change color attributes everyday on my Tumblr Theme

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This is my very first question.

I have a tumblr page, which i use for my daily sketches. It's mainly Black and White work, as I am colorblind ;-).

I've pimped the css and html so it fit perfectly with my taste. Now I am trying to add the very last touch.

I want everyday, the color background and text (caption+title) to invert everyday from Black to White… I know it can be done with Java. But I am not so good.

Any ideas ?

Thanks !

This is the tumblr page