What is the chemical composition of Turnbull's blue?
Though your textbook is right, Wikipedia isn't completely wrong as in aqueous solution, $\left(\ce{Fe3[Fe(CN)6]2} \right)$ gets converted and is in equilibrium with $\left(\ce{Fe4[Fe(CN)6]3} \right)$ (a redox change) and hence prussian blue and turnbull's blue are identical to look visually. But in a textual way, the naming is given as your textbook says, i.e. $\left(\ce{Fe4[Fe(CN)6]3} \right)$ is Prussian blue whereas $\left(\ce{Fe3[Fe(CN)6]2} \right)$ is Turnbull's blue.