I think it's a great idea: my first game, which I've never published, was based on the same idea :).. but you had to pick the color which was less used.. If it's becoming highly popular I'm going to feel bad never publishing it :)!
Re: There are ways to improve ranking position of my application?
I found it helpful to use tools as Mobile Action or App Annie, you can use them for free. It shows the impact of changing title/store text, I've gained some visibility but I agree with the others, and believe that downloads and...
I have a suggestion for your app discription.
"The principle is very simple, click as **** possible to win potatoes."
I would add one of the options below:
a: much
b: frequent
c: fast
d: slow
e: hard
f: loud
g: stylish
h: fanatic
The game itself is perfect. Very nice!