On the Subject of Switching Buttons

It's quite nice how the number of unique pairs matches the number of buttons. Too bad there'll always be a missing colour. :)

See Appendix of Directing Buttons for identifying modules in the _ Buttons family.

The buttons on the module will each alternate between two colours, with a wipe transition between them — the border of the wipe will be larger when switching to the first colour, as shown in Figure 1.

1st colour
2nd colour
Figure 1

Out of the sixteen possible pairs of colours, fifteen will appear on the module. Call the unused pair A.

One pair of colours will be used for two buttons. Call this pair of colours B.

For each pair X, X1 is its first colour, and X2 is its second.

Plug A1 and B1 into the table below to obtain a new colour, and do the same for A2 and B2. You now have a new pair of colours — press the button with this colour pair to solve the module.

B1, B2
RYGB
A1, A2RYBYG
YBRBG
GYBYR
BGGRR