The Fun Flag for Rhenium is based upon the colours and original German provincial coat of arms of the woman whom co-discovered this element, Ida Tacke. Ida Tacke was born in Rhine Province whose coat of arms feature a white wavy bend on green, as is the winding river of the Rhine. But for this fun flag, they serve as the background while the central shield colours are derived from modern Germany's flag. The other scientists who co-discovered this element were from different parts of Germany. Only Ida Tacke was born in a province named after the Rhine River, which is where this element gets its namesake, Rhenium - Element 75.
Not to be confused with element Rh, for Rhodium, which gets its name after the colour of a rose, assuming a red rose.