Why are Lanthanides colored?

1. The lanthanoids are present in the f-block of the periodic table.
2. They are present in the sixth group starting from $58\mathrm{to}71$.
3. They are transition elements and so they are placed far apart from the table.
4. They are first classified as "rare earth elements".
5. The lanthanoid elements first originate from the series lanthanum.
6. The unpaired f electrons will give color to the elements.
7. The f-f transition will allow a certain wavelength from the visible region which will be further absorbed and hence the color is emitted.
8. Example: Samarium imparts yellow color because of the presence of 5 unpaired electrons.