The central white pentagon denotes that this is a Western line of Longitude. Also the dominant upside down star denotes that this is a Southern Parallel.
The order of the colour to number is based upon the order of appearance in a rainbow. Orange is 2, because it is the second colour of the rainbow. Yellow is 3, since it is the third colour of a rainbow. Green is 4, because it is the fourth colour of the rainbow. Since there are only seven official colours in a rainbow, the numbers 8, 9, and 0 are coded to black, pink, and white; unless they appear in the pentagon or form the outline of the central stars of Latitude.
Image Credit: Wikipedia