in 1.14, armorstands with the marker:1b tag didn't glow, but whatever item they held/wore would glow, and this was important in model making of "custom mobs".

now in 1.15 neither the armorstand nor the model would glow, and if it is set back to marker:0b, both the armor stand and the model glow.

the model is placed in the armorstand's head slot.

1.14.4 picture is how the model glow is supposed to be

1.15 p1 picture is with armorstand marker:1b

1.15 p2 picture is with armorstand marker:0b