The spells Greater Invisibility turns a creature invisible:
You or a creature you touch becomes invisible until the spell ends. Anything the target is wearing or carrying is invisible as long as it is on the target’s person.
Do magical effects affecting the target, such as Crown of Madness's crown, Spirit Guardian's spirits, the Heat Metal's red-hot glow, and the Flame Blade's blade, also turn invisible?
Magical effects are not something the target is wearing or carrying. Normally the spell would need to say that it also turns invisible ongoing effects to do so. It does not. Therefore, it should not turn such effects invisible.
If you were having a magical light spell going, the light would still emanate. One interesting corner case would be disguise self - this might mean that the illusion from disguise self would not turn invisible (although I as DM would likely rule otherwise).
