Changing color of part of an image

I have a png image file that is partly opaque and partly transparent. I display it in a UIImageView as a mask of sorts over another UIImageView layered behind it (as a sibling subview of a common superview). It gives me perfect borders around something painted using a finger on the lower UIImageView in my stack of UIImageViews. Perhaps there are better ways to do this, but I am new-ish, and this is the best way I came up with thus far. None the less, my app is in the App Store and now I want to enhance it to provide more images to use as the mask of sorts over the finger painting. 开发者_StackOverflow中文版 But I don't want to bloat my bundle size by adding more static mask images as I did for the initial implementation. Not to mention I don't want to spend lots of time in photoshop making 100 masks. I'd rather programmatically change the color of the mask, without affecting the clear portion in the middle, which is not a simple regtangle or circle, but rather a complex shape. So my question is this: How can I change the colored portion of my loaded image without affecting the clear color portion in the middle? Is there a reasonably easy way to do this? Essentially I want to do what is described in this post (How would I tint an image programmatically on the iPhone?) without affecting the clear portion of my image. Thanks for any insights.

Have a look at the Tinted Image sample project. Try out the different modes until you get the effect you want.