NodeJS Sharp - Change the color of an image while retaining the transparency of the background

Nobody has claimed this yet.

for one of my projects, I need to change the color of an image based on the hex color chosen by the user. I managed to change the color of the image using Sharp, but I lose the transparent background. I would like help finding a solution to change the color of the image while keeping the background transparent.

Example GOOD:
[Old Color](https://i.stack.imgur.com/5cAqg.jpg)
[New Color](https://i.stack.imgur.com/Bh5mn.jpg)

Example BAD:
[Old Color](https://i.ibb.co/gW44RsB/Capture-d-cran-2024-02-29-103113.png)
[New Color background lose transparency](https://i.ibb.co/JyMMD6d/aa.jpg)

I don't have many solutions in mind, I've tried a few things that didn't work.

Here is my code:

```
const sharp = require('sharp');
const Color = require('color');

async function processImage(img, color) {
const cheminImage = img;
const couleurHex = color;

try {
const metadata = await sharp(cheminImage).metadata();

const data = await sharp({
create: {
width: metadata.width,
height: metadata.height,
channels: 4,
background: { r: Color(couleurHex).red(), g: Color(couleurHex).green(), b: Color(couleurHex).blue(), alpha: Color(couleurHex).blue() }
}
})
.composite([{
input: cheminImage,
blend: "multiply",
}])
.toFormat("png")
.toBuffer();

const image = `data:image/png;base64,${data.toString("base64")}`;
return image;
} catch (err) {
console.error(err);
return null;
}
}

processImage("./oldColor.png", "#383e42").then((result) => {
if (result) {
console.log('Base64 Image:', result);
} else {
console.log('Failed to process the image.');
}
});
```

Start with the processImage function and reproduce the result using oldColor.png, the supplied hex color, and Sharp's composite operation. Inspect the generated PNG's alpha channel and compare it with the linked GOOD and BAD examples; done means the recolored image retains the original transparent background.

Written by the indexing model from the issue text.