There's a series I watched when I was young, it was in the second half of the 80's, but it was already looking pretty old-school back then. It was not animation, most of the effect were done with miniature spaceships, and the characters were marionettes like the Thunderbirds.
A major feature in this show was that they were piloting some kind of star-fighter that could combine into a giant robot (Watch out, TV tropes link). I think the star-fighter and the Robot were Red (and maybe White).
The action was in space, and the story spanned across multiple episodes where they try to prevent someone from doing something when all planets of the solar system will be aligned. I think the alignment's date was planned to be the 31 December of 1999. Anyway I remember watching the particular episode (it left its mark on me) when the planets were aligning and they formed the robot for the occasion.