Subflow custom colours not applying since 4.1.6

### Current Behavior

See https://discourse.nodered.org/t/all-my-subflows-in-the-palette-have-changed-to-the-same-colour-after-4-1-6/100503

### Expected Behavior

_No response_

### Steps To Reproduce

_No response_

### Example flow

```
paste your flow here
```


### Environment

- Node-RED version:
- Node.js version:
- npm version:
- Platform/OS:
- Browser:
