Fix palette all white

[adaschma]

While testing the gnome47 port, I noticed that the "standard" Palette" only contains the color "White" (about 10x) and I am getting Errors in my log like:

  gnome-shell[3810]: [email protected]: "Gray" color cannot be parsed.

This is because the rgb values are not included in the gschemas.xml for the "standard" Palette while it is included for "GNOME HIG light" and other palettes. Using the rgb values from this webpage I added them to the "standard" Palette.