Hi, Faded_Dress! I just joined Craftster & did a search for "pysanky", which is how I found this question...and hopefully not too late.
I hope you still have your mixed dyes, because they do store! I have mine in Ball/mason jars, tightly sealed & stored upright, because you wouldn't want the dyes to spill. They are 2 or maybe 3 years old now, and this year they seemed to be fine. Sometimes, you'll notice that the dye comes out a little murkier than you'd like it to after a year or so--this especially happens with the yellow. If you add another tablespoon or two of vinegar, it should perk back up. Except don't put vinegar in the orange---the orange is a total weirdo, and will turn into a gelatinous mess if you add vinegar. All the other colors, I think, are fine with vinegar. Basically, if you had to add vinegar at the mixing stage, it will also help to perk the color back up. I'm going on my 3rd or 4th year, and I'm interested to see how long they'll keep, but so far so good. And when they finally need changing, The Ukrainian Gift Shop http://www.ukrainiangiftshop.com/
sells 'em for 75 cents a packet.