What is the "W" in this RGBAW color space matrix

### Type of issue

Missing information

### Description

That article helped me a lot to massively speed up an image invert and color change in powershell.
But what is the "W" in the color space here? I tried to find anything, but all search results link back to this article.

### Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.drawing.imaging.colormatrix?view=windowsdesktop-9.0

### Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.Drawing.Imaging/ColorMatrix.xml

### Document Version Independent Id

965b4c7a-083d-b594-f75d-e4f63b71e2e0

### Article author

@dotnet-bot