Suppose I want to mix a custom color on my own (with Brightside or Rustoleum)... I'm wondering about what type of measuring accuracy is required (and what types of measurement tools folks have used) to prevent visible color variations.

The situation I have is that I want to start out on a practice panel, but if that panel goes well, it is likely going to go on the vehicle. So, I'll be going all the way to the end steps on that panel. I don't want to mix up all the paint I'll need for the entire project at once. So, I'm trying to figure out what type of measuring accuracy I need if I mix the color in different batches.

As well, this would apply if I ever need to do repair work in the future on just one panel or one area of paint.

-- Dan