The colours and the letter-number is the Hasegawa code marking that clearly says which model is easy, which one is more difficult and which one has great details. Therefore the A, B, C, D and E letters. The digits next to the letters are the model number in the series.
Here the examples of the boxes for the same kit but released in different years.
the red strip 1977 ... A30
the blue strip 1980-1987 ... B2
the orange strip 1994 ... A05 and 2008 ... 00135 (A05)