According to ETKA, there only appears to have been four (standard) colours available for the floor mats. These are:
Soul (black) - 8A6
Indigo blue - 8B7
Light platinum (grey) - 8C8
Torrone (beige) - 8D9
This would also match what it shows in the brochure. Check out pages 44 and 45 of this document (
A8 - May 06.pdf) in the D3 Tech Dump thread.
One final check is to look at the build sticker in the boot. Go down to the section marked 'Paint No./Interior', and at the far right should be a two character code. Cross reference that with what is on pages 44 and 45.
Assuming of course that the mats haven't been changed at some point, then you should be able to identify the correct colour.
__________________
2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts
My DIY jobs -
Replaced alarm horn,
Replaced Coolant Temp sensor,
Updated RNS-D firmware,
Installed Reversing Camera and Digital TV,
Dashcam Installation,
Retrofitted Rear Blinds,
Auto-Dimming Rear View Mirror,
Chrome Boot Struts
Sold! 
2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights
My DIY jobs -
Fan Jet Windscreen Washers,
Retrofitted Electric Side Blinds