LCD Color Gallery
Transreflective LCDs reflect ambient light to illuminate the display, like classic Casio LCD wristwatches. The backlight is only needed to illuminate the display in the dark.
Transmissive LCDs require the backlight to be on for the characters to be visible, as no ambient light is used to illuminate the display. This also means if ambient light is bright (full sunlight), the characters will be difficult to see.
Positive versus negative refers to whether the the dots to create the characters are on and the background is off (STN+) or the character pixels are off and the background is on (STN-).
RGB backlight LCDs look cool but they have 18 pins compared to the 16 pins used in the HeaterMeter design. They will not work as the backlight pins are swapped compared to how the board expects them to be laid out.