#6 is a great basic design, but I think the colors could use some adjusting...
The Green arrow and the Gold building need to have some gradient / sheen to it!
Looks like the gold has some kind of gradient but I'm not sure if it's right yet...
The colors need adjusting:
Can you try a lighter gold color? (or maybe just increasing the gradient will work)
... and a darker green color? (again increase the gradient)
I've updated the sample images:
http://imgur.com/a/o5CLaLook at the colors of the buttons and make it resemble a simple classic calculator as much as possible.
Most calculators have only one red button...
It could be a double button (make it larger, like two of the buttons connected) on either the bottom left or the bottom right that would resemble a door.
Maybe make the window at the top white (currently black) and the top row of buttons light blue with gradient (currently white and red)... maybe all of the buttons except for the red one would be light blue with gradient (or white/gray/silver!) ... or black, with white symbols if that works better.
Symbols can include "1", "2", "3", "+", "-","%","x", "#", "*", "C" "M" and "=" or any combination.
Feel free to submit as many variations as you like.
Thank you!,
Kameron