Morse Code Flag of the Letter F - Foxtrot: . . _ .

The Morse Code flag for the letter F has an indigo, or dark blue, background.  Reason being, indigo is the 6th colour of the spectrum and F is the 6th letter of the alphabet.  The star, star, stripe, star reflects Morse Code's DOT, DOT, DASH, DOT.

Morse Code Flag for the Letter E: Echo .

Since E is the 5th letter in the alphabet it gets the 5th colour of the spectrum which is blue.   As Morse Code for E is a simple DOT, we only have one simple star. 

Morse Code Flag for the Letter D - Delta: _ . .

As green is the fourth colour in the spectrum and D is the fourth letter of the alphabet, we have a green background.  The yellow stripe and two yellow stars are reflective of the Morse Code for the letter D.  The stars and stripe are yellow because this colour is the contrast indicator for a green background.

Morse Code Flag for the Letter C - Charlie: _ . _ .

Morse Code Flag for the Letter C, Charlie.   This flag is yellow because C is the third letter in the alphabet and yellow is the 3rd colour in the rainbow.  Blue is the contrast indicator for yellow.  Thus the STRIPE, STAR, STRIPE, STAR indicates Morse Code for DASH, DOT, DASH, DOT.

Morse Code for the Letter B - Bravo: _ . . .

Since B is the second letter in the alphabet, it gets the second colour in the spectrum - orange.  Black is the contrast indicator.  Subsequently the stars and stripe that represent the DASH, DOT, DOT, DOT  are all black.  Remember that Morse Code Flags are always read downwards.

Morse Code Flag for the Letter A - Alpha: . _

The Morse Code Flag for the letter A consists of one star and one dash, which is reflective of one dot and one dash.  Since the letter A is the first letter of the alphabet it is coded to 1, and the first colour of the spectrum is red, consequently the background is red, and the contrast indicator is white.

Morse Code Flag Number Chart