Here we have the solution for the SLC correction.
For GRD we could use the name of the S1 products you are using as well as some processing if any have you done, as I don’t know which tutorial by ESA you mean. As always RD Terrain Correction, Calibration to backscatter and conversion to [db] should be obligatory. I write this because it doesn’t seem like db value example. I suggest to use regular Collocation from raster menu.
I am not sure about the RGB composition you made, I would recommend using master for green and blue and red for the slave with change…there you might see changed areas/flooded whatever in red instead of the result you are getting.
Petr