Axiom did a custom match for my paint. I sent a picture of the lid of the paint can that had all the numbers they needed. If you go to the website and pretend to buy something, you will see the fields available to also enter the custom paint information.
The colour-match fields aren't for the grill fabric, sadly. Debbie confirmed that there are multiple fabric options to choose from, but no option for custom fabric grille colours. I think what the site is asking for is the colour you'd like the frames to be (plastic edge that isn't covered by the grille).