Adjust shading of UITabBarItem

I have a set of white images that I am currently using as the images for UITabBarItems in a UITabBar.

These images are shaded automatically, and I would like to adjust this shading so that the icons do not appear as dark as they do by default on the iPa开发者_如何学编程d.

I don't see anywhere to adjust the shading intensity in the nib file -- is there any way this can be adjusted?

---

Ended up creating another set of images.