Colour of  ${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+2}\mathrm{and} {\left[\mathrm{Ni}{\left(\mathrm{en}\right)}_3\right]}^{+2}$  respectively will be

${\mathrm{H}}_2\mathrm{O}$ is a weak field ligand.
$\therefore {\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+2}$……. Absorbs longer wavelength …. emits green colour 
Ethane 1, 2–diamine is a strong field ligand.
$\therefore {\left[\mathrm{Ni}{\left(\mathrm{en}\right)}_3\right]}^{+2}$  …… absorbs shorter wave length ….. emits violet colour.