For what it's worth, here's a photo of the deck. Note the unwashed section on the left.

Here is a link that might be useful:

Unfinished IPE turns grey from exposure to the sun.--Bleaching of surface. This is true of all woods over time. If using pressure washer on any wood, make sure to set for wide stream and keep tip several inches from wood to prevent etching or fraying surface.

Wood can be restored since damage is quite shallow. Follow procedures for restoring surface on any wood deck. Coat with a semitransparent tropical hardwood stain when done to preserve color. Otherwise process or turning grey will start again.

The pressure washer was set for the least pressurized (widest) stream of water that actually got the gunk off the deck. I honestly don't know what you mean by "follow procedures for restoring surface on any wood deck." The procedures are different for different woods. And ipe is NOT meant to take stain, as I understand it; it's too hard of a wood and won't soak in the stain. Those who have used stain on ipe tell me that they need to reapply literally every year. Maintenance headache... So what's the right thing to do, here? I'm not sure I mind the grey (though the reddish natural color is amazing), but I would like a more uniform look. Should I just wait for the wood to re-weather?

It looks normal to me. Just let it continue to weather to a uniform grey color. A thorough cleaning once per year is also good. I prefer a stiff bristle push broom, and scrub brushes with a good deck cleaner, then a thorough rinse with the garden hose.

Agreed, that looks pretty normal to me as well, just let it weather back uniform again. It looks like it is the the graining of that piece where it's most visible. If you don't want the maintenance don't stain it, otherwise you will be coating it once a year or more. If it's driving you nuts you can try a 2 part cleaner/brightener system for hardwoods (Messmers and Woodrich make them).

We had to clean my dad's Ipe deck after 3 years of not cleaning it and letting the stain wear off. Here's the link the photo of the cleaned deck below for comparison...the mistake I made was "sweeping" my power washer back and forth instead of walking it up and down the boards with the grain (I had it too close to the wood) and even on the lightest nozzle it left marks, so be careful with that also.

Here is a link that might be useful:

Wow... your deck looks amazing! Did you apply the Woodrich cleaner yourself, or is it the kind of thing best left to a professional (such as a painter)?