When Ethane-1,2-diamine is added progressively to an aqueous solution of Nickel (II) chloride, the sequence of colour change observed will be : 

${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}_{\left(\mathrm{aq}\right)}^{+2}+{\mathrm{en}}_{\left(\mathrm{aq}\right)}\to {\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4\left(\mathrm{en}\right)\right]}_{\left(\mathrm{aq}\right)}^{+2}+2{\mathrm{H}}_2\mathrm{O}$
Green
${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4\left(\mathrm{en}\right)\right]}_{\left(\mathrm{aq}\right)}^{+2}+{\mathrm{en}}_{\left(\mathrm{aq}\right)}\to {\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_2(\mathrm{en}{)}_2\right]}_{\left(\mathrm{aq}\right)}^{+2}+2{\mathrm{H}}_2\mathrm{O}$
 Pale Blue 
${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_2\left(\mathrm{en}\right)\right]}_{\left(\mathrm{aq}\right)}^{+2}+{\mathrm{en}}_{\left(\mathrm{aq}\right)}\to {\left[\mathrm{Ni}(\mathrm{en}{)}_3\right]}_{\left(\text{aq }\right)}^{+2}+2{\mathrm{H}}_2\mathrm{O}$
Blue / purple