Color Splash Studio (http://www.macphun.com/colorsplash) is a new Mac app designed to offer let you create photos with selective colors. It requires Mac OS X 10.6 or later, costs US$0.99 (for a limited time) and is available at the Mac App Store in the Photography category.
Color Splash Studio offers a variety of adjustable parameters for color layer, including saturation, hues, exposure, brightness, contrast and blur. You can choose between grayscale and sepia for a monochrome layer.
Color Splash Studio has adjustable parameters for the amount of monochrome layer. There’s a selective blur for both color and monochrome layers and a customizable brush that lets you adjust diameter, opacity and softness
Color Splash Studio integrates with Aperture and iPhoto albums. It supports most image formats — including RAW files and resolutions of up to 32 megapixels — and boasts built-in sharing via Facebook, Flickr, Twitter, Tumblr or email.