In what fluid does the sperm swim in the oviduct?
Specifically in the fallopian tubes, the fluid is called tubal fluid, and is produced by the innermost mucosal layer of the tubes (specifically, the peg cells in the epitelium)


In the follicles, there is the follicular fluid, liquor folliculi.
In the uterus, the endometrial fluid.
In the cervix, cervical fluid.


I don't know about the color. For what it's worth, cervical fluid varies from white to yellowish, but it's transparent when it's best for spermatozoa to swim.