Niobium is an elemental metal and is strong yet flexible and is slightly heavier than 316L stainless steel. Niobium is chemically non-reactive. Few people are sensitive to niobium.
Niobium jewelry is available in a range of colors which are produced through anodizing, not dyeing. During anodizing, the jewelry is submerged in an electrolyte solution and voltage is applied. Anodizing creates an oxide layer on the jewelry. The color results from refraction of light through the oxide layer, and the thickness of the layer determines the resulting color.