The green coloured borax bead obtained from copper salts is

When copper oxide reacts with boron trioxide then it forms cupric metaborate. The reaction is given below:

$\mathrm{CuO} + {\mathrm{B}}_2{\mathrm{O}}_3 \to \mathrm{Cu}{\left({\mathrm{BO}}_2\right)}_2$

Due to the presence of ${\mathrm{Cu}}^{2+}$ ions $\mathrm{Cu}{\left({\mathrm{BO}}_2\right)}_2$ gives green colored borax bead.