diff --git a/core/modules/filters/colour-ops.js b/core/modules/filters/colour-ops.js
index 1a3e5dae6..4e0e514f0 100644
--- a/core/modules/filters/colour-ops.js
+++ b/core/modules/filters/colour-ops.js
@@ -40,6 +40,11 @@ exports["colour-set-oklch"] = makeSerialColourOperator(function (colour, operato
 	return colour.display().toString();
 });
 
+exports["colour-set-alpha"] = makeSerialColourOperator(function (colour, operator, options) {
+	colour.alpha = $tw.utils.parseNumber(operator.operand);
+	return colour.display().toString();
+});
+
 exports["colour-contrast"] = makeParallelColourOperator(function (colours, operator, options) {
 	var colourContrasts = [];
 	$tw.utils.each(colours,function(colour,index) {
diff --git a/editions/tw5.com/tiddlers/Colour Handling Improvements Preview Build.tid b/editions/tw5.com/tiddlers/Colour Handling Improvements Preview Build.tid
index edbf3f283..d9527fe7a 100644
--- a/editions/tw5.com/tiddlers/Colour Handling Improvements Preview Build.tid	
+++ b/editions/tw5.com/tiddlers/Colour Handling Improvements Preview Build.tid	
@@ -24,6 +24,7 @@ modified: 20250204130756749
 * [[colour-contrast Operator]]
 * [[colour-best-contrast Operator]]
 * [[colour-interpolate Operator]]
+* [[colour-set-alpha Operator]]
 
 ! Other Features Included in this PR
 
@@ -38,6 +39,7 @@ The following features are required for the new colour handling system, but are
 
 The code for the palette compilation process can be found in $:/core/macros/CSS. The following tiddlers are generated by the compilation process:
 
+* $:/palette is the current palette tiddler
 * $:/temp/palette-consolidated is the result of merging the current palette with the chain of imported palettes. The palette entries are the raw values such as `<<colour background>>`, not the computed colours
 * $:/temp/palette-colours is the result of computing the colours for the current palette. The palette entries are CSS colour values that can be used directly