OP: All good advice here -- and don't move forward without confirming the moiré problem at 100%, as dbmoore recommends.
I would add to Léonie's clever advice that you will get even better results brushing in the "Color Monochrome" adjustment than you'll get with the (misnamed) "Black & White" adjustment.
Somewhat frustratingly, the Color Monochrome brick does not let you sample a color from your image. ("Hello? Apple? Pass Auf!") ... so here it gets a wee bit twicky:
Use the Color Brick eyedropper to assign the color of the t-shirt to one of the available six slots. _Make no adjustments with the Color Brick_. In fact, you can "uncheck" the Color Brick adjustment.
Then activate the "Color Monochrome" Brick. Note that clicking the color swatch brings up the OS X color picker, whereas clicking the drop-down arrow brings up an Aperture-specific color picker. Click the color swatch. In the OS X color picker, click the magnifying glass (for consistency, this should be an eyedropper, but some of the runnels in the orchard are ahead of others). Using your mouse cursor, which should now be a magnifying glass, click the square color sample you created in the Color Brick. Brush this over the moiré. Lower the intensity of Color Monochrome Brick as much as you can without introducing any moiré.
Sell your print.
NB: if anyone knows a better, quicker, more direct way to do this, my ears are as the ocean to its many rivers.
(Added: Can you post the RAW file somewhere?)