When I look at products that are sold in liquid form, at least half of them come in opaque bottles or containers. This gives the package designers more freedom, since you’re starting with a clean slate and don’t have to worry about the product itself showing through, or the impact of ambient light that passes from one side of the bottle to the other. But there’s a downside: consumers have no way of telling how much product is left in that bottle.

However, I saw a clever solution to this problem. The laundry detergent we buy comes in the typical white bottle that you can’t see into. But there’s a thin strip of clear plastic running down the side, so you can easily tell how much detergent is left. While it may add a few cents to the production cost, this approach strikes an excellent balance. Product marketers and designers can make the bottle look however they want, while consumers can see when it’s time to buy more — without any guesswork. I’m surprised this approach hasn’t been widely adopted, especially when coupled with a call-to-action on the bottle that encourages customers to buy the same brand again.