paintRack is an app available for Android devices that helps you track what paints you own, what paints you want, and what paints you used on that model you haven't touched in 6 weeks.

You can stand at the paint rack in your local store and scan the bar code to see if you already own a color!

It is an indispensable tool for me.

Not sure what the rules are for posting links to 'paid apps' so I won't but you know how to find it.

I am not affiliated with the app in any way except as a happy customer.

J--

Good advice, in addition to the idea "that there is an app for that!" you may also consider:

A good old notebook, you can even dab a bit of paint down as to help colour match.

There are also a few electronic notebook applications that would also serve well. (Evernote or MS Notebook for example). You can also add photographs or video of the process.

I recommend paintRack as well. Although I've gotten behind on properly marking everything out in the Sets area.