The fields in the flags are coded to numbers. In this case the field of red, white, and blue reflect the Z number of Dubnium: 105. The violet stripes indicate we are in the 7th period, since violet is the 7th colour of the spectrum. Since Dubnium is in 5th group, the white and blue horizontal stripe reflect this association. White is coded to zero and blue is coded to 5.
Dubna is a place in Russia, near Moscow where wonderful ground breaking nuclear research took place.