The order of energy absorbed which is responsible for the color of complexes.
(A) [Ni(H₂O)₂(en)₂]²⁺
(B) [Ni(H₂O)₄(en)]²⁺ and
(C) [Ni(en)₃]²⁺  is 

E_absorbed = C > A > B
${\left[\mathrm{Ni}(\text{ en }{)}_3\right]}^{2+}>{\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_2(\mathrm{en}{)}_2\right]}^{2+}>{\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4\left(\mathrm{en}\right)\right]}^{2+}$
Number of bidentate ligands are decreases, then its crystal field stabilisation energy decreases. Hence E_absorbed also decreases.