Our save the dates were different from our wedding colors/theme, we purposely chose something different since we wanted our invitations to for sure match our wedding colors so when the photographer takes detail photos it'll blend with everything
Mine are my wedding colors, your invitations set the tone of your wedding in my opinion.
Of course they don't have to be anything but what you want. There are no set rules on what wedding invitations need to be, but it's true that most people use their wedding colors. However, if you don't want to use them, then don't feel pressured to do so. I personally used my wedding colors in my invitations, just like a lot of other things, such as the save the dates and wedding programs. I was even able to get a free sample from Magnet Street of what they would look like in person before ordering them all: https://www.magnetstreet.com/wedding-invitations