If they are in the same product it is easy.
Just open the first band and then go to the layer Manager and add the other band as a layer.
In the view, I show reflec_12 with algal_2. If you want to colourise the second layer you can open the band in a second view and use the Colour Manipulation Window.
In the Layer Manager you can change the transparency for each layer and you can also swipe the content.
The Layer Manager is accessible from View -> Tool Windows