Best Mac Photo Editing Software For A Beginner?

I just started getting into photography. My setup so far is a T4i with the 18-125 STM lens and a 55-250 IS II lens. I'm fine w/ the sharpness of both lenses for now, but I do want more color. I figured my options are buying better lenses or buy an image editing program to get more color from my images. I currently use iPhoto & Pixelmator, but these seem to be all-or-nothing propositions (can change colors, but can't target areas to change the colors easily). I have enjoyed Pixelmator's free tutorials, so any software that provided a similar service would be ideal. Currently I'm thinking Aperture, but that's more because I'm familiar w/ iPhoto, not because of any features I want from it. Any suggestions that might be good for my use?

I mostly shoot pet and city shots, so I'd like to be able to enhance the sky in city pics and eyes in pet pics w/o changing the colors image-wide. Any input would be great. Thanks