Due to the translucent quality of ink, when printed over a transparent stock, the ink colours will be see-through and might look a lot lighter than they do when viewed on your 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 like a white piece of paper will make the colours appear more vibrant/denser/closer to how they look in your proof.
If the sticker is placed over dark coloured objects, this can affect how visible the printed design will be.
If you place the sticker over clear glass or a window, the colours can appear very light and will be the most see-through. (If the sticker is meant to be put on the inside of a window but read from the outside, the artwork will also need to be inverted.)