How to set Emissive Entity texture now?

Hi, so before to set a emissive texture for an entity all you had to do was doing a hole black texture, and leave colored the parts you want to be emissive, but now this dont work anymore - this will make the hole non-emissive parts black, its a pain to try/error how dark should be the rest of the texture to match the color you want of the original texture.. how do you guys are doing that now? how you make the emissive texture?