This I was watching some tutorials about VOPs and the basics of building custom shaders.
Although VOPs are another quite overwhelming topic, after some trial and error I managed to build a shader from scratch that has a base color which you can enable/disable and can take in a color map which you can enable/disable.
First I thought I was doing something wrong since I wasn't able to see the texture on the model but then I just tried rendering it and there it was , the texture renders just fine.
So how do I build a shader that is capable of OpenGL?

go to Edit Rendering Parameters dialog for your material/shader

from SHOP Options add OGL tab with all properties to your shader, then connect whatever you need with your shader parms with expressions as it's the case in default materials

I tried it but now I seem to realize that my OpenGL isn't working at all.
I don't get an OpenGL preview of my texture from any shader, why is that? (display textures is enabled)

Make sure to have UV. Try the attached

Also check that Display Texture is checked in Display Options/Texture

Now it works. I changed nothing just opend your scene and now it works.

Edit:
I just realized that the path was wrong. For some reason it was set to $HIP instead of $JOB.
Sorry for the trouble :roll:

A good way to debug textures is to use the pictures that ship with Houdini e.g. $HFS/houdini/pic/butterfly1.pic