first I have a tube which gets colored in the inside. but I want it on the outside.

Secondly i want to cut a hole in a plane. Same as in cars where you can put your coke can into to fixate.
Many thanks

I am not sure what could be the cause of your color problem, but it is easy to make a hole or cupholder.

First, start with your plane (subdivide it if neccessary).

Select the vertices that make up a square (as shown below).

Choose To Sphere under Mesh Tools. In the pop-up box hit ok with 100% selected.

Then keep the circle selected and add the center pixel to your selection. Hit ‘E’ to extrude and select 'Region". Extrude down a few times.

Finally, apply Subserf (Modifiers - Add Modifier) and Set Smooth (Link and Materials - Set Smooth).

Hope this helps,

If the tube doesn’t have thickness then you can’t have seperate materials on each side of the same face.

Give the tube some thickness and assign the material to the outside faces if that’s the problem.

Thanks JvIasterMind

Cyborg Dragon now i’ve the same with a cube. The color shows only on the wrong side, the correct side (outside) is transparent. Where can i add thickness? Before I had it once fine…

If it’s UVMapped then Recalc Normals Outside, Ctrl-N with All selected in Edit mode.