Here's a story of another color -- red -- including explosions, isotopes, unpaired electrons, and radioactivity.
Burning elements is still important in fireworks and also in modern analytical chemistry techniques such as ICP-MS. Also, a fair number of elements are named after their colors: chlorine, rubidium, cesium, chromium, rhodium, indium, iridium, iodine, etc.
The depiction above implies how weakly rubidum holds its outermost electron and why it so readily gives it up to become Rb+. Most anything can pluck it off. Here's a spectacular video of rubidium hitting water:
Naturally occurring rubidium has two isotopes: the stable 85Rb (72.2%) and the radioactive 87Rb (27.8%). 87Rb is considered only "slightly" radioactive--despite its abundance (it is naturally present in seawater)--because of its extremely long half-life of 1010 years. Remember that something has to actually decay in order for it to emit radiation.