I started out to say that deliberately trying to build a stash is a good way to tie up money that might be more wisely spent (or invested/saved) elsewhere.
However, I've also noticed that sometimes a certain color is almost impossible to find at times. It seems that some years almost all the manufacturers have similar colors in their lines - and other years some colors seem to be unavailable.
Aqua being an example - I had shades of aqua from at least four lines - and they coordinated perfectly.
I've noticed that the "Christmas Reds and Greens" have changed over the years from Crayola Red and Green to a darker yellowed green and the reds also seem to have darkened.
So the colors that are popular and/or available do change over the years.