There are many reasons why a paint match will not match the original colours on the vehicle in question. Paint tends to discolour after time due to ultraviolet radiation or UV. Sometimes the clear coat may not be right or the tint they used was not right. Most of the time an insurance company will only match your original paint after that it becomes custom and with custom tints it is very hard to match unless you have the original formula mixed exactly the same as the new one.