Rolleiflex filters

I am normally shooting slide film, but thinking about improving my b&w as well. In this regard I am considering getting a yellow filter, and perhaps a UV filter. I have a few questions:

Can the UV filter be used with color film? There's a website that says no.

What kind of effects can I expect from the yellow filter? I would like slightly darker skies, and maybe better skin tones (not that it currently looks bad, but I want to try different options).

Yes, you can use a UV filter with color print and slide film. Generally you don't need one unless in the mountains or at the beach. I like them for protection of the lens. There is a big argument about this. Some feel that the extra glass can degrade your image or even damage the lens if it is dropped with filter attached. I've never found a problem with quality filters like Contax, Heliopan, B+W, the best Hoyas, etcetera. Do you like Ford trucks or Chevy, Nikon or Canon, beer or wine, blah, blah, blah. It's one of those never ending arguments.

With b&W film, Yellow filters yield a little darker and more normal looking skies. They also enhance skin tones for a more natural look. I encourage you to try one.

I do advise you to buy a polarizer and learn how to use it. I think it is the most valuable filter that you can own. It works with both color and b&W.

A UV filter has a very slight yellow cast.
Using it for color negative, you're never going to see a difference because processing of the film and then printing
are going to have more effect then is noticeable.
IF you're shooting slides there's going to be a very slight cast that MAY be noticeable. If you're looking for
a more accurate color, no filter or a Skylight would be better.
With that, the effect of either filter won't be seen unless you put a slide shot with each one
side by side on a light box.

I never take bw photographs outdoors without a color filter. Usually Yellow, large format often with orange. I have a rolleicord and the only filter i have is red, so i use that. Indoors, i never use a filter, hardly any point.
All my 35mm lenses have a yellow filter on them that usually stay. I have UV filters for each lens also, just in case. Alan Gales advice i have followed for years in 35mm. I feel if the lens drops and strikes the edge, the filter will take the blow, and save damage to the lens especially the filter threads, and likely the glass.
You are using a rolleiflex, which has a lens cover. So you are not able to leave a filter in place and use the lens cover. You will be mounting the filter each time you take the camera out. seems a bit inconvenient, but should get used to it. Get any of the BW contrast filters, if possible yellow first, and always use it. If a UV shows up, get it in case you want to take color. I don't have one, and shot slides once - they came out ok but wish i had a filter anyway. If you want the hard contrast of blue sky, consider getting a red filter, but remember it will make exposures longer than yellow by at least a stop or 1 1/2.
I am no pro, or expert, but this is best practices and it has served me well. I don't like blank clear skies - they need to be there in my opinion, and the contrast is sacrificed in the remaining image with the general blue/uv scatter in shadows that the film will respond to.

Actual Rollei brand filters are fairly common if you search around on line. The "gelb mittel" (middle yellow) is the equivalent of a No.8 and I use one all the time with black-and-white film if sky or foliage is involved. It took me years to find a light red filter, and I've used that in the landscape recently to great effect separating clouds and sky. It has a bit subtler effect than the typical dark red.

You will see the cloud seperation only when you have blue sky other than that the yellow, organe and red filter will have no effect on skies.

To my knowledge there exist only light red filter which is rare and expensive.

I got a polariser in Bay I for less than 20 euros.

The only way you'll know if a particular filter works for you is to test it. Each film has its own spectral response. And each user wants different things in the final image. I usually shoot ACROS with no filter and Delta 400 with a green/yellow filter. I also tested medium yellow, orange, light red, and green.