You want us to buy your app to give you feedback as a favor?
A better way to approach this would be by giving away promo codes as a means to get feedback.
if you have promo codes would be better.
But im not paying .99$ to try your app out for you.
Depends on how you setup your UI. If you used IB, then you can just set the images on the tabs. IIRC the images are 30x30 and grayscale works fine since iPhone makes the images "blue" anyway. You should definitely check out the tab bar doc -- it'll do a better job of explaining it than I can. You could also ask in the developers forum here on MR.