If the lanthanoid element with xf electrons has a pink color, then the lanthanoid with $(14-\mathrm{x}) \mathrm{f}$ electrons will have the colour as:

Color imparts by the compounds depends on the number of unpaired electrons. The maximum number of electrons present in f subshell is 14. Lanthanoids usually shows color because of the f-f transition. Both xf and (14−x)f  have the same number of unpaired electrons. Hence, they both show same colour.