It should be noted that this is abusing unclamped Color3 values. This could very well break in the future, if Roblox decides to clamp Color3 values for whatever reason!!!
Fairly recently, I discovered a pretty neat trick. You can turn a boring emissive texture that doesn’t have any effect and make it bright and glowing - like neon!
This applies for pretty much everything that has a Color3 value and is technically a 3D object - such as textures and decals - this trick doesn’t work for parts, however, since the BasePart classes automatically assigns a BrickColor value based on the currently present color.
Anyways, to have emissive textures working, you’ll simply need to have a texture’s Color3 value set to something way above 255, like so:
This makes any texture or decal you have assigned come out like this:
Here’s what the texture looks like set to 0,255,255 instead of 0,9999,9999:
The higher the number, the brighter it becomes.
To have textures layer properly, you’ll simply need two parts - one with the emissive texture (without a background) and one with the Abedo / Diffuse texture like so:
It’s reccomended you have the emissive texture be around 0.02 - 0.05 studs above the abedo texture.
This is a good work around for now until Custom Materials are implemented. It sadly does not work for MeshParts, however.
Hope this tutorial helped some of you! 
ParticleEffects and SpecialMeshParts with out-of-range VertexColor values are similarly affected, sometimes even glowing in 2 different colors in ShadowMap mode (one of which is actually a blown-out neon shadow)!
