Plum Crazy color ?

Many factors can change the way a color looks. Humidity, air pressure, and spray technique all affect the way a color looks and the metallic lays. If it's sprayed dry or at a higher pressure it will be lighter than if it was sprayed at a low pressure or wetter since the metallic will tend to stay near the top and not 'sink'. Older paint will tend to bleach out a bit with time and sun, especially single stage metallics. Plum Crazy did not hold up very well in most cases and many cars had to be repainted when they were fairly new.

These colors were all single stage when new. Using bc/cc affects the color also as the clear makes the metallic look more pronounced. There are also variations between paint brands. Another factor is the mixing pigments have changed over the years, so there will be a slight variation due to this also.

Yes, there are scanners for automotive paint. Sometimes they get it spot on but the paint store will only guarantee a 'blendable match'.
Dallas