So you had your colors done a while ago--10, 20, 30 years--and you wonder if you need to have them done again.  The answer is "yes."  Your hair color has probably changed.  You've aged.  Your overall coloring might have softened.  Your preferences have changed.  Look at these two fans, both done for the same woman. 

The one on the bottom was done in 1986; the one on the top in 2010.  Notice how the colors in top one are softer, not as bright, a bit darker.  This client came to me to get a few extra colors added to her older fan.  But the new fan suits her so much better that she purchased that complete new fan to use instead of the older one.

So if it's been a while since you've had your colors done, it's time for a touch up.