EDIT: Oh, wait, holy shit. This ribbon is multicolor — you can see the red stripe on the ribbon, and apparently the Remington Travel Riter Deluxe does support multiple colors on a ribbon.
I think that it’s the lever in the upper right on the front that switches color.
EDIT3: You know, decades ago, I remember fiddling with my dad’s typewriter. It had a selector lever there too. Could never figure out what it was for, seem to recall that it adjusted the height of the hammers, which seemed pointless. He only had a black ribbon, but I bet that it supported a multicolor ribbon, and that’s what it was for. Never did resolve that mystery until now!
That typewriter probably doesn’t support color, but apparently some had a ribbon with multiple colors and the ability to select among them.
https://old.reddit.com/r/typewriters/comments/1jnie9o/can_someone_pls_tell_me_why_my_typewriter_has/
This guy is using it to do color accents with typewriter art:
https://www.youtube.com/watch?v=_bqi2qY918M
EDIT: Oh, wait, holy shit. This ribbon is multicolor — you can see the red stripe on the ribbon, and apparently the Remington Travel Riter Deluxe does support multiple colors on a ribbon.
https://www.ebay.com/itm/133756651478
EDIT2: Here’s the manual:
https://site.xavier.edu/polt/typewriters/RemingtonRandTravel-RiterDeLuxe_Manual.pdf
I think that it’s the lever in the upper right on the front that switches color.
EDIT3: You know, decades ago, I remember fiddling with my dad’s typewriter. It had a selector lever there too. Could never figure out what it was for, seem to recall that it adjusted the height of the hammers, which seemed pointless. He only had a black ribbon, but I bet that it supported a multicolor ribbon, and that’s what it was for. Never did resolve that mystery until now!