Bug in getBackgrounds() using custom theme colors - google-apps-script

Question

I've got a spreadsheet with colors from a custom theme.
When I read the colors using getBackgrounds() the colors returned are all #000000
If I read the colors cell-by-cell using getBackground() the colors are returned correctly.
If I use standard colors (ie not colors in my Theme) the colors are also returned correctly.
TEST SHEET
(available to view at https://docs.google.com/spreadsheets/d/1nCZeUbCjs_5p6_52v8ggqVgrgnJ-Pd6x-gzXUFfV8G0/edit?usp=sharing
Cells A1:D1 contain the names of the four Beatles, all with background color #b70906
TEST CODE
/** #OnlyCurrentDoc */
function getbackgroundstwoways(){
var fullrange= SpreadsheetApp.getActiveSpreadsheet().getRange("A1:D1");
// Read all cells using getBackgrounds
var arBack = fullrange.getBackgrounds();
var arValues=fullrange.getValues()
Logger.log("Full array " +arBack + arValues);
//Now do the cells individually with getBackground
for (var i=0; i<fullrange.getLastRow();i++){
for (var j=0; j<fullrange.getLastColumn();j++){
Logger.log("Single cell " + i + " " + j + " " + fullrange.offset(i,j).getBackground() + " " + fullrange.offset(i,j).getValue() ) ;
}}}
LOGGER OUTPUT
Full array #000000,#000000,#000000,#000000John,Paul,George,Ringo
Single cell 0 0 #b70906 John
Single cell 0 1 #b70906 Paul
Single cell 0 2 #b70906 George
Single cell 0 3 #b70906 Ringo

Answer 1

How about this answer?
Issue and solution:
When I saw your shared Spreadsheet, the background colors of cells "A1:D1" has the color type of "THEME". I think that this is the reason of your issue.
In the current stage, it seems that getBackground() can directly retrieve the background color from the color type of "THEME" as the hex string. But, it seems that getBackgrounds() cannot directly retrieve them. The retrieved values using it becomes #000000. I'm not sure whether this is the bug or the current specification. But in the current stage, the background colors of the color type of "THEME" can be retrieved by the methods in Spreadsheet service.
One of several solution is to use getBackground() as your script. This has already been achieved in your script.
In this answer, as another pattern, the colors are retrieved from the values retrieved by getThemeColors. The flow of this script is as follows.
Create an object for searching the colors from the theme color type.
Retrieve background objects.
Retrieve the background colors from backgroundObjects.
Sample script:
function getbackgroundstwoways() {
const ss = SpreadsheetApp.getActiveSpreadsheet();
const fullrange = ss.getActiveSheet().getRange("A1:D1"); // Range from your script.
// 1. Create an object for searching the colors from the theme color type.
const theme = ss.getSpreadsheetTheme();
const themeColorObj = theme.getThemeColors().reduce((o, e) => Object.assign(o, {[e]: theme.getConcreteColor(SpreadsheetApp.ThemeColorType[e]).asRgbColor().asHexString()}), {});
// const fullrange = SpreadsheetApp.getActiveSpreadsheet().getDataRange();
// 2. Retrieve background objects.
const backgroundObjects = fullrange.getBackgroundObjects();
// 3. Retrieve the background colors from backgroundObjects.
const backgroundColors = backgroundObjects.map(r => {
return r.map(c => {
if (c.getColorType() == SpreadsheetApp.ColorType.RGB) {
return c.asRgbColor().asHexString();
} else if (c.getColorType() == SpreadsheetApp.ColorType.THEME) {
return themeColorObj[c.asThemeColor().getThemeColorType()];
} else {
return null;
}
});
});
console.log(backgroundColors);
}
This script can be used for the color types of both "RGB" and "THEME". When this script is run at your shared Spreadsheet, [ [ '#b70906', '#b70906', '#b70906', '#b70906' ] ] can be seen at the log.
Even when the RGB types and the THEME types are mixed, this script can retrieve the background colors as the hex string.
Note:
In this case, the background colors are retrieved from the theme colors. But when you overcoat the background colors as the RGB type of #b70906, you can retrieve them using getBackgrounds().
When I searched about this that getBackgrounds() cannot be used for the THEME color type at the issue tracker, I couldn't find this. So how about reporting this? Ref
Please use this script with V8.
References:
getSpreadsheetTheme()
This method is added at December 18, 2019.
Class SpreadsheetTheme
getBackgroundObjects()