Follow Up question to "Multiple Background Images" thread

Hello,

I am trying to add the ability to switch between background images on a watch face (A cool graphic for my Venu, with the option of a blank/simple background).  I found this thread on the boards: https://forums.garmin.com/developer/connect-iq/f/discussion/1150/watch-face---multiple-background-images

The thread is 7 years old and I now have some follow up questions. 

The post has the code:

function checkLoadedImage() {
if ( isDaytime && !daytimeImageLoaded ) {
pic = null; // This is included to show that memory is being cleared. You don't actually need it.
pic = Ui.loadResource(Rez.Drawables.day_image);

- On the last line here, is "day_image" the actual file name ("my_image.png") or is it the "id" as defined in the layout.xml? (Yes, I am using layout.xml).

- How do I remove the background image if I just want to replace it with a solid color?

- Also, the first line checkLoadedImage()...I cannot find the source for this in the Toybox.  Does it still exist?  What does it do?

Thanks!

This is where I am at on my first Garmin watch face (I've done a couple on Fitbit). 

 A is for an alarm set.  N is for active Notifications.  The Zulu time can be switched to steps.  Battery power display can be turned on or off. It is the gray shaded background I want an option on.