In the previous version of QGIS when you loaded a multiband color image into raster calculator the bands were separated.
In version 3.6 I am only seeing 1 band how do I get the other bands displayed ?
I think it is a bug in QGIS 3.6, if you load the raster into QGIS 3.4.5 Long Term Release (LTR), it will be loaded correctly with all the bands available in single raster:
QGIS 3.4.5 LTR:
You can report a bug following this page here: Bugs, Features and Issues. My advice is to use QGIS 3.4.5 LTR as it is a stable version.
I can confirm this has been fixed in QGIS 3.7.0 (the current development version) and so will be in QGIS 3.8 when it comes out.