Sometimes you got your color in color file and you want to use that one.
WHAT YOU CAN DO IS THIS CODE BELOW
fab.setBackgroundTintList(ColorStateList.valueOf(Color.parseColor(getString(R.color.youcolor))));
As you know to change it programmatically, you need to use setBackgroundTintList(), then pass the ColorStateList.valueOf() which is required and this one take a certein int and parse it... 
Note: if you just put the int color right away it could give you problems to get the color you want sometimes and for that reason i don't use it and don't recommend it to use it like that
Then put within ColorStateList.valueOf(), Color.parseColor() this is what you need to put...
This needs a String but you have the int color in the color file, so what to do?
Within Color.parseColor() pass getString(), this is a method that each activity has, so within getString() you put finally your color as this R.color.yourcolor