[docs] Undocumented `'default'` color

[emlai]

Some components (at least IconButton and Chip) mention 'default' as the default color:

But the meaning of this color value is not explained anywhere in the docs. The other color values are explained in the palette documentation.

[mnajdova]

Thanks for pointing this out. In v5 we had an effort for removing all default values for the color prop, but in these components it seems like there is some kind of default color that is different than the rest. In my opinion we should rename it to something more descriptive, for example in the IconButton it seems to be none or transparent. I am adding the issue for the v6 milestone, as renaming the prop would be a braking change.

[vctqs1]

Thanks for pointing this out. In v5 we had an effort for removing all default values for the color prop, but in these components it seems like there is some kind of default color that is different than he rest. In my opinion we should rename it to something more descriptive, for example in the IconButton it seems to be none or transparent. I am adding the issue for the v6 milestone, as renaming the prop would be a braking change.

I get issue when upgrade theme from MUI v4 to v5, do you have any docs related to remove default value in color props