There are problems with Beacons rendering the beam color, the beam will have a the default color (white) in the inside of the beacon but outside it will be the color (the stained glass you chose).
There are problems with Beacons rendering the beam color, the beam will have a the default color (white) in the inside of the beacon but outside it will be the color (the stained glass you chose).
First of all, that's a (unsupported) modded server
Secondly, the beam only changes it's color, once it enters the stained glass, this is intended