If the square part of the bathroom wered a little larger, I'd go with using a border. But being that any border will disappear either under or behind the toilet, it seems like it'd be wasted. My suggestion would be to do a solid floor, maybe in some kind of eye catching pattern-- something like a hopscotch or diagonal pattern for bigger tiles, or maybe something in the way of a herringbone for smaller rectangular tiles. No matter how you do it, though, I think with the way your bathroom is shaped and the size of it, a border really wouldn't have the effect I think you're looking for.

I thought the same thing before reading Bill's comment. Tiling on a diagonal & adding some blue accents to the mix could look really nice. Just a thought about the little hallway, have you considered putting a niche and some glass shelving in that wall? Depending on how deep you can make it, it could be a nice way to display candles, soaps or what nots. Just a thought. :c)

I'm crazy for borders and whenever I do a floor, I incorporate some kind of a border. I can't help myself. In your bathroom I would run a border an equal distance from the wall, from the face of the vanity and from the tub and then I'd jog it into the hallway if you want it to feel like one larger room or not if you want to articulate the hallway as a separate little space . I think those idiosyncrasies of the border jogging are part of what makes them fun though. Here is a picture of my border following the shape of a knee-wall bumpout to accommodate plumbing (still not finished but close!):

And my tiny potty room, yes, part of the border is concealed - I don't mind!

better picture of the border, bathroom less finished:

And my kitchen floor plan with the border following every corner:

This border is maybe more intricate than what you're after, but it shows that jogs and angles can be dealt with by a DIY'er.
Laid out dry-fitted:

WC detail:

Blue,

I had the same thoughts as lukkiriish on the niche. Lisa may put borders in every floor, I am putting niches everywhere I can! :>) (Recessed medicine cabinet counts as a niche- right?).

What about doing the border as if it was a rug, and have both sides in front of the toilet, making a little jog, and then ending at the edge of the vanity? Or, how about incorporating one of those mosaic pieces 'as a rug' in front of the vanity?

Because your toilet projects out into the rectangular "hallway", if your border were just a long rectangle the border would be partially covered by the front foot of the toilet. The disruption of the pattern can lead to visual clutter, so to speak.

Because of that I'd have the border jog around the back of the toilet and follow the walls. Sure, the border will then be covered by the rear foot of the toilet in that case, but that's to be expected, plus it's not in the main sight line when you walk in the room.

All that said...the heavier and more contrasting the border is with the field tile, the more it will accentuate the narrowness and length of that initial "hallway".

Thank you all! I love those floors, Casey and Lisa!

My new toilet has a slightly smaller footprint than the old one. The new vanity is also an open vanity with a slatted base (you can see the tile floor a little, but not too well). Pic:

I'm sort of thinking about a rug/border? Any more pix?

Blue
P.S. New lights are going in tomorrow -- I'll finally make some progress on the world's slowest renovation.