I'm pretty sure that there aren't any rules for the color of bathroom towels! You can do whatever you like. IMO it's nice if the towels are solid colors, and if there are not more than two coordinating colors out at the same time. You could choose one or two of your favorite colors in the tiles and match those.

When I was trying to decide which color to select from Restoration Hardware, I chose about eight colors and ordered one washcloth in each color from RH. That enabled me to see which were the prettiest. It also gave us quite a large stock of washcloths! I matched the towels to my favorite colors in the decorative tile strip in the combination bath/shower, buttery gold and lavender. They look great.

I always use white towels at all times everywhere, they seem to pop no matter what the decor is. I used to color match with towels but I ended up moving a lot and being stuck with colors I no longer needed.

I also use white sheets only, I guess I'm a hotel and spa kind of person, lol.....

there's an amazing array of colors available so I must be in the minority.

I have more than a dozen sets of towels, in all different colors (except white; my white towels are ancient).

Here's how I would answer your questions:

If the bathroom has colored tile in the shower area, are the bathroom towels supposed to be the same color as those tiles? And, if so, are they supposed to be darker color or lighter color than the bathroom tiles?
I would choose a coordinating color towels. For example, if the shower tile is light blue, I'd get dark blue towels. If the tile is dark, I'd get light towels.

But, what if the tile color was white? Then, you'd simply pick a white towel or do you want a colored towel to make it pop?
I'd get colored towels that coordinate with the decor of the rest of the room.

And, what happens if there are several different colored tiles in the shower area? Do you try to match the lightest color, medium color, or darkest color?
I'd pick the color I like best and get towels in that color. Or I'd get towels in each color and mix-and-match them.

Or, are you supposed to pick towel colors on the basis of the wall color in the rest of the bathroom, not the tile color?
Assuming that the walls and tiles don't match, I'd get towels that go with both if possible. Or I'd paint/paper the walls to coordinate with the tile and go from there.

Here is a link that might be useful: towels in many colors in my bathroom

What colors are you working with? If I had a navy and white bathroom, I'd get red towels, yellow towel, orange towels.

I agree with mitchdesj. Nothing is more luxurious than big, fluffy white towels and they look fantastic with any color scheme. No stress! I always shop the white sales. Last year at this time I bought some fabulous 100% Egyptian cotton towels (Renaissance by Christy) from Bloomingdale's...on sale + additional discount from some coupon + free monogramming!

I just bought new towels and re-painted my bathroom. I painted the walls Silver Sage like the bedroom, but I knew I wanted pink to go with it, so I bought both pink towels and also ones to match the wall color. My cabinets and tile are white, so I can pretty much do anything as far as accent colors.

What color tiles and wall color are you working with? What style are you going for in the bathroom?

daisy, I would love to see your pink towels with your Silver Sage. I've used light blue, yellow and white, but didn't think of pink. I bet it's gorgeous.

There are no rules. You can choose whatever you like. Do you have a pic of your bathroom?

Link
for Brutuses.

I think Marvin was having a little marvelous fun here!

I am redoing a guest bath, and was thinking how I used to always match the shower curtain to the towel to the mat etc etc and how especially in the guest bath, they get so little use. For the new decor, I think I am seeing the light and will mostly go with white towels and a few accent colors. It will be nice to be able to mix them up. (and by the way, I have little luck with keeping the vibrant color towels vibrant so white is sounding lovely to me)

Here's what I'd do: Buy bath towels in the colors you're considering. Take them home, drape the different ones over your towel racks and pick what you think looks best. Return the ones you don't want and get full sets of the one you do.

I agree that dark or brightly colored towels do fade so I prefer to stick to lighter colors myself.