Thanks guys for your help. Here's an update- I'm gonna post it here because somebody may come accross my problem in the future and do a search.

So I called around to lots of MB-specialized upholstery shops and they are all confused. None of them are familiar with code 265 leather mushroom. They all tell me that the only two colors for my model and year are cream beige and palamino.

So I followed some advice from a member on another forum and sent an email to classicparts@mbusa.com, and they emailed me the following info sheet for my car (the responded within a day, which was great). See the interior code in bold/underline:

VEHICLE IDENT. NO: WDB 124051 1B 192939
VEHICLE IDENT. NO: WDB EA51DX LB 192939
VEHICLE MODEL : 300 CE-24
TYPE OF BODY : COUPE
ORDER NUMBER : 0 0 705 20704 DISPATCH : 12 02 1990
PRODUCTION NUMBER: 5030427 8 PAINT 1 / 2: 702
ENGINE NUMBER : 104980 12 006930 _ TRIM : 265
TRANSMISSION NO. : 722359 03 346518 _ TIRES : MICHELIN
RADIO SERIAL NO. : BE1480A95161959 _ HEADLIGHTS : BOSCH
WIPERS : BOSCH
OPTION CODES : 222 240 241 301 412 420 430 446 461 494 519
524
531 543 551 570 581 592 600 639 800
CODE DESIGNATON
702U SMOKE SILVER - METALLIC
265A LEATHER CREAM BEIGE - MUSHROOM / QUARTZ
222 RIGHT FRONT SEAT, ELECTRICALLY ADJUSTABLE
240 OUTSIDE TEMPERATURE INDICATOR
241 LEFT FRONT SEAT ELECTRICALLY ADJUSTABLE WITH MEMORY
301 STORAGE BOX IN THE REAR
412 ELECTRIC TILTING/SLIDING ROOF IN STEEL VERSION
420 4-SPEED AUTOMATIC TRANSMISSION
430 HEADRESTS IN THE REAR
446 440+441+442
440 TEMPOMAT (CRUISE CONTROL)
441 STEERING COLUMN, ELECTRICALLY ADJUSTABLE (202/170/168 MECHANICALLY)
442 DRIVER'S AIRBAG
461 INSTRUMENT IN ENGLISH
494 CALIFORNIA VERSION
519 BECKER RADIO GRAND PRIX ELECTRONIC CASSETTE - USA
524 PAINTCOAT PRESERVATION
531 AUTOMATIC ANTENNA
543 SUN VISORS WITH VANITY MIRRORS, ILLUMINATED
551 ANTI-THEFT/ANTI-BREAK-IN WARNING SYSTEM
570 FOLDING ARMREST FRONT
581 AUTOMATIC CLIMATE CONTROL
592 GREEN HEAT-INSUL. GLASS, ALL-AR., HEATED REAR WINDOW PANE, BAND
FILTER
600 HEADLAMP WIPER/WASHER
639 634+636
634 ELIMINATION OF FIRST AID BOX
636 ELIMINATION OF WARNING TRIANGLE
800 MODEL YEAR 1990

So they used different color names for the different materials... I'm assuming my leather is called mushroom, while the vinyl on the doors is called cream beige... and the color of the vinyl on my dash is quartz. Do Deanyel, you were exactly right!

So I guess that settles it- the formal name for the vinyl I'm looking for is actually cream beige. Very interesting! I sent away for a sample of cream beige... that will tell me for sure!!

Thanks so much for your help.