Its not the colour of the fluid that is detected, its normally the shape or the actual container. Rumrunners are basically a plastic container that is not detectable by the x-ray machine, the chances of finding one is purely down to luck or having a 'suspect' object in your case.

"Rum Runners" (flexible plastic flasks) are designed to bypass cruise ship security by mimicking the density and appearance of water or clothing on an X-ray scanner. Unlike glass bottles, which have a very distinct "hard" silhouette, or metal flasks that trigger metal detectors, these heavy-duty plastic pouches are virtually invisible when tucked inside the lining of a suitcase or hidden between layers of dense clothing like jeans. Because they contain no air pockets, they don't slosh noticeably, and they are durable enough to withstand the pressure of stacked luggage. Furthermore, most cruise ship security is primarily looking for weapons and large "hard" contraband; a soft pouch filled with clear liquid often looks like a toiletry bag or simply part of the bag's structure. However, in 2026, cruise lines have become more sophisticated, often using "density sensors" or random hand-searches of bags that appear "unusually heavy" for their size. If caught, the alcohol is confiscated and usually destroyed, though some lines may hold it until the end of the voyage for a small "processing fee."