Invisible ink: it is colorless when it under the daylight or sunlight, However, you could see the beautiful color under the uv light. here is the following information.

Printing type:

The Invisible ink could divide into Offset printing, screen printing, gravurepriting.

UV Invisible Ink

Color: Colorless to Yellow, Colorless to Green, colorless to blue, colorless to red and so on.

Package: 1kg/can, 12can/carton.

Show you the effect of  UV Invisible Ink

Under the sunlight

As you could see in the picture, when the invisible ink under the sunlight, it will look transparent  

When the Invisible Ink under the uv light, the invisible ink which is on the left one is colorless to yellow, the right one is colorless to green.

Variable color for your choice