Textures in Renderman?

Hi, I’ve started trying textures in renderman but I can’t achieve the result I want.
I would like to change the color of the texture(using a color ramp node or normal diffuse node or whatever) and I’ve tried doing that by adding a pxrGamma node between the RGB output of the texture node and the diffuse input of the pxrDiffuse node; that didn’t work, so I’ve tried added a pxrRamp instead.
In both cases the texture disappears from the mesh and the color is not applied.
Any clue of where I’ve gone wrong?