If you have a typical CZ, you didn't have NIGHT SIGHTs, but the standard sight which is painted with a luminescent paint that will glow if charged with light (for about 10 minutes.)
Had there been tritium sights installed, you would have a HOLE in the area if the tritium vial has broken, or a glass surface that isn't glowing. If the inset area is now the same grey/black as the rest of the sight, the paint has just fallen out. (If there were tritium sights, it would likely say so on the box the gun came in -- if you still have it.) Factory tritium sights are pretty rare on CZs; they're sometimes added by distributors or the custom shop.
Get some white and green model paint, mix up a small batch to a shade you like, and use a toothpick to drop a small amount into the recessed area. (you should probably refresh the dots on the rear sights, too, while you're at it.) Using a different color on the rear sights might be a good idea -- maybe the same color as the front sight, but with a bit of YELLOW added.) Clean the top of the bottles, the caps, seal them tightly, and you'll have enough to touch up those guns and others for years to come. (Total outlay will be about $5 +/- $1).
NOTE: Testor's make flurosecent model paints, and if you can find it, that works really well with gun sights. As does clear nail polish once you get a color you like, as a top coat.