Ugh, I've brought this up before in a forum post, but I can't find it and we can't search forum posts.
But, you've got it wrong. It's the color of the background of the scratch-off side of the card. Those front and back images in our database are actually only one side of the card. The scratch off side is not shown. I've asked Admin to fix it but they haven't.
1970 Topps Scratch Offs have a white background, 1971 have a red background.
Someday my cards may double in value and then be worth half of what I paid for them.