I created a pattern in Illustrator and now I want to export as a PNG including the artboard which is grey. The problem is that the background won't save as grey in the PNG, it's either black, white or transparent. Does anyone know how to save the grey background as well in the PNG? (pattern is just an example)
The Artboard can only be exported as black/white/transparent when you create a PNG.
The only way for you to use a different colour is to simply make a layer behind your artwork and fill it with a rectangle of your chosen colour.
To use a colored background actually make a colored background.
Place a rectangle of color over your art board and behind your other objects.
The art board is not supposed to be viewed or provide colors. It is considered neutral, behind the scenes, like the actual canvas surface behind a painting.