I’m sure this will be old news to many but Adobe have a nice little free web-app to help designers (or anyone else for that matter) select a colour scheme. The app was previously known as Adobe Kuler, but has since been re-branded as Adobe Color CC.
The nodes on the neat little colour wheel can be easily dragged around the palette to create a set of complimentary colours.
You can even use an image or photo to create a colour set. You can drag the dots around the image to sample to colours within, or you can use the ‘color mood’ dropdown to automatically generate a scheme.
Once you’re happy you can save and share your scheme, and it can be synced to other Adobe applications such as Illustrator, Photoshop and InDesign. There’s even an app available for iPhone/iPad users.
Check it out at color.adobe.com