Hi ... I have an idea for an alternative to the Red-Green bars...

a radar-map:
http://i.imgur.com/o4DvoYo.jpg

on one axis you have Buy orders and on the other you have Sell orders...

I think its easier on the brain to understand - than the current Red-Red-Green-Green diagram which is VERY confusing for for first time users.

And eventhough i think i know what they mean - i still mixup their meaning because i forget what up and down is...
X/Y diagrams and radar maps are easier to read - in my oppinion.  
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Edit:

Alternatively, the BUY and SELL colors should be different ... so instead of each having 2 colors - the placement above/under indicate what they are...

Green above = increase in buy
Green below = decrease in buy
Red above = increase in sell
Red below = decrease in sell

using the same color for 2 schemes makes the graph harder to read

or maybe i havent spent enough hours getting used to what is what...