Hi - thought I'd share an idea I have used to keep track of paint colours in our home.
When you paint a room, do a good sized sample of the paint used on the INSIDE of the light switch cover. Write the paint brand, name and special details (1/2 stregth, etc) under the paint on the inside as well with an artline pen.
If you want to colour match years later you just have to take off the switch cover and read the info - or take it in and the guys at the paint store can use the paint sample to colour match for you.
Its the only way I've worked out to not lose my paint colours !