Hi, I do some test in Cycles and I have this issue :
But 2 previous RGB mix work :
I don’t know why the last RGB mix doesn’t work.
All RGB mix are setup to Mix and 0.5
Thanks a lot for your help.
What are you trying to do exactly?
Cycles does have a node limit when using SVN (as the more nodes you put in, the slower the shader and the more pressure you place on the hardware, especially GPU’s.).
If it’s what I think you are doing (making a procedural tiles texture), then you’re making things way too complex (just use the bricks node or an image texture).
Yes, what is it that you’re trying to accomplish? For regular tiles, bricks can do the job (a separate one hooked up to a noise can make each tile have a unique color, which can be used to create three random numbers - which I typically use to drive texture coords for an image texture, inaccurate lay normals etc).
For more advanced tiles, I have setup my own nodegroup, where I get per tile texture coords, random color, mask, gradient, corner sharpness, and I can even set random rotation and chance of this kicking in. So this is fully possible to setup. I would suggest however, to use the bricks&tricks plugin or synaGlows tiles (lots of variations to play with).
Hi and thanks for your answers.
This great riddle “man what do you do” 
it’s simple experimentation to do a real blur system. Each layer increase a blur. But it’s not interesting here.
This issue is an enigme for me and I’m very curious to know why. Why after some recurrence Mix RGB outpout is black.
Again, thanks for your time and interest.
Use Window->Toggle console (on windows, start it from the console on the other platforms) and re-render, there’s probably a warning about running out of svm stack space on there.
@LazyDodo you are a pro. “Cycles: out of SVM stack space, shader too big”
I never see “SVM stack” in my Blender life so I learn one more thing with you. Thanks a lot !