grout colorant question from noob

I could tell a long sad story here about how I had created a beautiful mosaic garden with a birdhouse for my Carolina Chickadees, lots of mosaic terracotta pots, a special stepping stone among the ordinary ones...and then my entire garden (not to mention most of my house) was crushed by Tropical Storm Bill in 2003. It must have affected me more than I realized, because I am just getting back into my mosaics now, 8 years later. (The exact date of the disaster was June 30, 2003.) So...here's my question...how long does an unopened bottle of Plaid Emerald Green Make it MOSAIC Colorant (for grout) last.???

Got it from Michael's, I think. I would have just bought more, except today I went to Michael's and I could get mosaic grout in any color I liked as long as it was white or black.

Sigh...I realize that Home Depot would have more choices but if you knew the traffic between me and Home Depot you would know why I'm shivering even though it's 90 degrees. :-)