Check color in Google Sheets - google-apps-script

Question

I'm struggling a bit with Google App Script. I'm looking to write a simple script that checks when a user changes a colour, and, if it's wrong, corrects it.
Here's my code so far:
function onEdit(e) {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getSheets()[0];
var r = sheet.getActiveRange();
if (r.getBackground() != '#D9EAD3') {
var ui = SpreadsheetApp.getUi();
ui.alert('Wrong colour!');
r.setBackground('#D9EAD3');
}
}
It almost works...However.
it only works when text is changed, not colour (there doesn't appear to be an onFormat option)
it appears to change cell a1 every time.
Can anyone help? Thanks.
EDIT
That's a great help - thanks, Sandy. My code now looks like this:
function formatWasChanged(e) {
var r = e.range;
if (r.getBackground() != '#D9EAD3' && r.getBackground() != '#FFFFFF') {
var ui = SpreadsheetApp.getUi();
ui.alert('Wrong colour!');
r.setBackground('#D9EAD3');
}
}
I've also defined this as a project trigger, called on change. Unfortunately, it's still not running when I test it on my spreadsheet - var r = e.range; appears to fail when I run it in the console.

Answer 1

You can also use an installable "Change" trigger. That can check for:
Quote from Google Documentation:
e.changeType - The type of change (EDIT, INSERT_ROW, INSERT_COLUMN, REMOVE_ROW, REMOVE_COLUMN, INSERT_GRID, REMOVE_GRID, FORMAT, or OTHER)
Note the FORMAT type of change.
Google Documentation - Change Trigger
You must click the 'Resources' menu, and choose 'Current Project Triggers' in the code editor.
function formatWasChanged(e) {
Logger.log('e.changeType: ' + e.changeType);
if (e.changeType === 'FORMAT') {
Logger.log('Its a FORMAT changeType: ');
};
};
If you do stay with the onEdit() trigger,
Don't use:
var r = sheet.getActiveRange();
To get the range that was edited, use:
var r = e.range;
Google documentation:
e.range - A Range object, representing the cell or range of cells that were edited