Due to the translucent quality of ink, when printed over a transparent stock, the ink colors will be see-through and might look a lot lighter than they do when viewed on screen. This will be affected by the surface you end up placing your transparent sticker on.
For example, placing the transparent sticker over a white surface will make the colors appear more vibrant/denser/closer to how they look in your proof. If the sticker is placed over dark colored objects, this can affect how visible the printed design will be.
If you place the sticker over clear glass or a window, the colors can appear very light and will be the most see-through.