If the location is very wet then you should only use a calking that is specifically for this type of area. I usually use a high grade silicone specially formulated for tubs and wet locations. The only place I can imagine on one of these units that would fit this bill is between the tub and a metal/glass door unit. In these locations I only ever use clear, as it assumes the colors of what is behind it. If you aren't an expert calker then buy an extra tube and practice on some scrap wood or something and/or seek more advise/tutorial on methods and techniques. If you "work" (tool with your finger etc.) silicone to any large degree then all you will end up with is a big smeary mess.
For incidentally wet areas, like between the fiberglass and the tile floor or walls, then I use Phenoseal vinyl adhesive calk. This may be made by DAP, I don't remember. It is fairly universally available and I love it. You can use their "translucent" flavor or one of their wide variety of colors. This calking can be tooled with a fine damp sponge or finger to get a perfect seamseal.