My bathroom has the same sort of tile, and I just used River Mist by Valspar.

I have some jewelery in a similar color that mixes ivory and dull turquoise with those colors.

We moved into a place with that exact tile and we ended up painting the walls Sherwin Williams Electric Lime. It's definitely not for everyone, but we love it.

If you'd like the accent color to look more like a color and less like a neutral, you should look to the opposite side of the color wheel. That suggests blue, as the first commenter did. I would also consider aubergine for a pretty interesting combo. That would help shift the tile back to white, of that's what you're after.
http://www.awcolor.com/

What kind of feeling do you want to invoke? If you want a spa-like atmosphere, think about aquas and summery blues. If you want something more exotic, think aubergine, like AmySRQ said, or a deep blue. I recommend staying far away from anything with yellow undertones.

I agree with using a complementary color. A blue gray or lavender with gray overtones would be nice. You could go either light for a more spa like feel, or dark for a dramatic effect.

I would play off the blue hue that the glass blocks evoke.

They look very similar to my tiles that I got from Home Depot. I agree with the group and go for cool tones like blues or greens - my wall is paired well with sea foam.

Pale aqua or seafoam is generally a good choice for a bathroom. Or a soft dove grey. Maybe an apple green though, which would go well with the cabinet color. My bedroom is Laura Ashley Apple 4. Whatever you do, I'd grab a couple of samples first and see what you like with the lighting in the bathroom. The color I painted my bath looks great with natural light but terrible with the lights on, so I'm going to be repainting it.

I was about to suggest a blue/aqua color too! I like the way the glass appears blue in your photo and think it looks great next to the brownish shades.
In the long run, I'd retile.

I like your idea of playing off the darker border tile--paint walls that cocoa brown to match, and maybe add accents of silver, in the form of a large mirror, (so the dark paint color becomes almost a border around the large mirror)--this would tie it in to the glass blocks. You could even (if you're up for it) re-stain the vanity and med cabinet darker, or paint with silver leaf paint. Travertine, to me, evokes a "spa" feeling, so why not play up the spa-ness of it by having fluffy white towels, and maybe a white waffle-weave shower curtain? You could add some teak accessories like a wooden bath mat, or a small teak stool, too.

My Mom just renovated her bathroom with a travertine in the same color. She painted the room navy. It looks amazing.

Have you thought about painting the tiles? I painted the tile backsplash in my kitchen with a white enamel spray paint. It turned out great, and it even solved the grout problem (the problem being the porous nature of grout -- gross!) I would suggest you paint the bath surround white, which would make the floor more of an accent color rather than the dominant color, and you could bring a wider range of tones to the walls and the cabinetry. White tiles... dark brown cabinetry... very very pale blue/gray walls... white fluffy towels... it could work!

Adding, when I painted my tiles, the rough grout still looked like grout even though I used a shiny paint.

Decide what you want from the shower curtain, and then work from there. If you are dead set on adding color and need some pattern in the room, maybe you could pull a color from the pattern of a multi-colored shower curtain, but frankly it doesn't look like the room is huge enough to benefit from being broken up into contrasting chunks of color. I'd find a shower curtain in a metallic look like bronze or copper, and paint the walls to coordinate with the tile trim around the window.

We're painting our guest bathroom with travertine in Tea Light by Benjamin Moore.

I know this isn't the most exciting suggestion, but I think you should paint it white. Not off-white or cream, but true white. We have a lot of travertine, and I think it looks best when it's simple. It has an inherent rusticity to it for me, and whenever I try to go for a color, it ends up looking too faux-Mediterranean for my taste.

I would stain the cabinet and mirror something darker (or preferably change the mirror, because I am not a matchy-matchy girl, but it's not bad), paint the walls white, use turkish towels and a rough, natural linen or burlap shower curtain and call it a day. Simple and clean without trying too hard.

Congrats on your new house, and good luck!

I agree with white, it might not be very exciting, but it will look bright, clean, and tie in with the bath, sink, grout and window frame. If you are desperate for colour add it with accessories you can change like towels. Painting the walls a contrasting colour like blue/green will make the room appear smaller, busy for your eye and therefore not so calm or relaxing.

For a neutral, earthy look I'd go with a warm deep taupe on the walls and add a textured shower curtain. You might want to check out some of the good tips here:
How to Solve 11 Common Decorating Problems with Color and Pattern.
or check out this site about How to Choose and Use Color.
I have found both of them helpful. Good luck. Let us know what you decide and if possible post a picture when you've finished the room. I'd like to see how it turns out.

Dark blue!

White walls with some green plants. All green bathroom walls could give your skin a greenish tint and make choosing the right lighting a real nightmare.

Home Depot and most high-end paint stores have color matching computers - go play with one or two of them! They will show you complements, lighter & darker shades, accents and other ideas.

Do you have an extra tile or two? Take it to a paint store and have the color-matching computer look for compatible colors for your travertines' hue.

If you have no spare tiles, then bring home paint-cards and pick three that match your tile's colors. Then take those swatches back to the paint store and play with the color computer.

I totally agree with bright white. Adding blues or aquas with a shower curtain would look really crisp then.

Farrow and Ball "Setting Plaster". It's a light tan/pink that looks kind of rustic.

I think your bathroom looks fine as is. Mabe set some fluffy white towels on the edge of the bath.