[ $Eu^{2+}$ ]-activated barium magnesium silicate phosphor, $(Ba,Ca)_{3}MgSi_{2}O_{8}:Eu_{x}$, has been known to emit blue-green light. In this study we report the manufacturing processes for producing either pure green or pure blue light-emitting phosphor from the same composition of $Ba_{2-x}Ca_{2}CaMgSi_{2}O_{8}:Eu_{x}$ (0 < x < 1) by controlling heat treatment conditions. Green light emitting phosphor of $Ba_{1.9}CaMgSi_{2}O_{8}:Eu_{0.1}$ can be produced under the sample preparation condition of highly reducing atmosphere of $23\%;H_2/77\%;N_2$, while blue or blue-green light emitting phosphor under reducing atmosphere of $5~20\%;H_2;/;95~80\%$ N_2. The green light-emitting phosphors are prepared in two steps: firing at $800~1000^{circ}C$ for $2~5$ h in air then at $1100~1350^{circ}C$ for 2-5 h under reducing atmo­sphere $23\%$ $H_2/77\%;N_2$. The excitation spectrum of the green light-emitting phosphor shows a broadband of $300~410$ nm. The emission spectrum has a maximum intensity at the wavelength of about 501 nm. The CIE value of green light emission is (0.162, 0.528). The pure blue light-emitting phosphors can be produced using the $Ba{2_x}CaMgSi_{2}O_{8}:Eu_{x}$ by introducing additional firing step at $1150~1300^{circ}C$ in air before the final reducing treatment. The XRD analysis shows that the green light-emitting phosphor mainly consisted of $Ba_{1.31}Ca_{0.69}SiO_{4}$ (JCPDS $#$ 36-1449) and other minor phases i.e., $MgSiO_3$ (JCPDS $#$ 22-0714) and $Ca_{2}BaMgSi_{2}O_{8}$ (JCPDS $#$ 31-0128). The blue light-emitting phosphor mainly consisted of $Ca_{2}BaMgSi_{2}O_{8}$ phase.