we need to be clear of the description. It’s hard to troubleshoot with “green” 
Green? Blinking Green? Green on the Tinker App? Green on the RGB LED? 
Let’s do this:
Factory reset the core
Send Wifi Credentials using Tinker App
See if the core goes from Blinking Blue to Solid Blue then Blinking Green to Breathing Cyan (RGB LED on the core)
Let us know what is the RGB Led colour you are stuck at
Yeah de RGB led on the core went from blinking blue to solid blue then blinking green to breathing cyan. After that I programmed it. No problem about that. But for me the colour in Tinker App is green,but I can use the Tinker App and I can see the name of my Core.
I think that my problem is next. I saw if I program the Core… I can´t work on pins by tinker (appears 404 Error). If I want to use Tinker I ´ve got to “Reflash Tinker”, erasing my program in the core and after I can use the Core by Tinker.
So I think I didn´t understand how Tinker and Core work together, did I?? Do Tinker and Core work as I explain in previous paragraph???
Ok good to know that your core is working fine!
If you want to use the Tinker App to control the 
core, you need to program it with the Tinker app.
Downloading other firmware you wrote will not allow Tinker App to control it (partly true)
You can add in the following template for your own firmware if you want to use Tinker functions.
Can I use the Tinker functions with my own program with this template???
I´m sorry about my messages… previously I thought the performance of Core and Tinker were different. Many thanks everybody!!
Yes, like i mentioned, the link above contains the basic template with tinker functions as well
You can copy the entire code into a new App in Web IDE, add on your own code then flash it to the core.
Have fun!
@sparklingdevil, think of Tinker as a demo user application on the Spark Core. When you flash your own program to a Core, Tinker is overwritten. Because Tinker is open-source, you can use all or parts of it in your own program. @kennethlimcp provided a link to the Tinker program so you could use and modify it as needed.
You’ll notice that there is are setup() and loop() functions, much like Arduino. You will also notice that Tinker uses Spark.function() to do the control magic on the pins. Feel free to add your own code in there and experiment to learn more. Some member has extended Tinker’s functionality so you may want to search the Community to find some ideas. 