I agree with @Carmie — there is no real expiration date for colored sugars because sugar is a natural preventer of bacterial formation, so as long as you keep your supplies dry, you should be fine to continue using them. On the website for Cake Mate, one of the leading makers of colored sugars, it states that its colored sugars and nonpareils have an average shelf life of 36 months, but that is simply to guarantee the freshest product. The following guide to the expiration date sequence is also provided:
Locate the code date on the container of your item, which includes a letter and a couple of numbers (example D6038). The first letter of the code is the month (A=January, B=February, etc.) and the following digit is the year. A product with a code of D6038 was produced in April (D) of 2016 (6).
ETA: Wilton is another popular brand, but it uses a different numeric approach for dating its products using the year and day of manufacture. For example, if you have an item with a code of 18064, the "18" means it was made in 2018 and the "064" means it was made on the 64th day of the year—so the item has a manufacture date of March 2018. Here's a quick guide to the days of the year broken out by month:
January = 1-31
February = 32-59
March = 60-90
April = 91-120
May = 121-151
June = 152-181
July = 182-212
August = 213-243
September = 244-273
October = 274-304
November = 305-334
December = 335-365