K3[Co(NO2)6]= Yellow ⇒Co3+=3 d6⇒t2 g6eg0 $\begin{aligned}
& \mathrm{K}4\left[\mathrm{Fe}(\mathrm{CN})8\right]=\text { Yellow } \Rightarrow \mathrm{Fe}^{2+}=3 \mathrm{~d}^6 \Rightarrow \mathrm{t}{2 \mathrm{~g}}^6 \mathrm{e}{\mathrm{g}}^0 \
& \mathrm{K}_3\left[\mathrm{Fe}(\mathrm{CN})_8\right]=\text { Bright Red } \Rightarrow \mathrm{Fe}^{3+}=3 \mathrm{d}^5 \Rightarrow \mathrm{t}{2 \mathrm{~g}}^5 \mathrm{e}{\mathrm{g}}^0 \
& \mathrm{Cu}_2\left[\mathrm{Fe}(\mathrm{CN})_8\right]=\text { Chocolate brown } \
& \mathrm{Zn}_2\left[\mathrm{Fe}(\mathrm{CN})_8\right]=\text { White }
\end{aligned}$ Spin only magnetic moment of complex having Yellow colour is zero.