This alphabet is the opposite of gray and dreary. This alphabet will be all about colour, LOTS of colour, nothing BUT colour. Both the foreground and background of every letter photo should contain nothing but colour -- NO BLACK, NO WHITE, NO GRAY. It doesn't matter what colour, but whatever colour it is, it needs to be saturated enough so that it really doesn't "look" gray (or white or black).
With the holidays and the new year coming, how about something "festive". Could include letters of the season, such as ones with Christmas-y stuff (holly, berries, seasonal colors); winter letters (with snow or ice on the letters); sparkly letters (don't have any like this, but I assume they're out there); letters with sparks, rainbows or other features. This could be far-fetched, but the emphasis is on fun and celebration.