https://photoshop-api.adobe.io/v2/create-composite doesn't support customer fill color. But document says it does

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Which topic?

https://developer.adobe.com/firefly-services/docs/photoshop/guides/photoshop-v2/v1-to-v2/document-creation-migration#creating-a-basic-blank-document

### What's wrong with the content?

The fill field changed between V1 and V2

Two breaking differences: (1) "backgroundColor" was renamed to "background_color" — the V1 string enum "backgroundColor" is invalid in V2. Use "background_color" (with underscore). (2) Custom solid colors require the object form in V2 — V1 only supported the three string shortcuts, V2 adds {"solidColor": {"rgb": {"red": R, "green": G, "blue": B}}} for arbitrary custom colors.

I tried solidColor. Doesn't work.

My payload:
`{
"image": {
"width": 1920,
"height": 1080,
"resolution": {
"unit": "density_unit",
"value": 72
},
"fill": {"solidColor": {
"red": 255,
"green": 255,
"blue": 255}
}},
"mode": "rgb",
"depth": 8
},
"outputs": [
{
"destination": {
"url": "url",
"storageType": "azure"
},
"mediaType": "image/vnd.adobe.photoshop"
}
]
}`

### What changes do you propose?

_No response_

### Anything else that can help to cover this?

_No response_

Start with the linked document-creation migration page and compare its V2 fill examples with the reported create-composite request body. Verify the documented custom-color shape against the API behavior, then update the page so the supported field and payload syntax are unambiguous.

Written by the indexing model from the issue text.