This is referring to the layer of flat colour that it provided for subsequent printing / writing operations; because this ink is crcuail to the durability of the disc, it is often printed at the disc manufacturing stage, to provide a buffer layer agains whatever ink might subesquently be used for labelling etc.

I am unaware of a specific specialist term, but have not carried out any exhaustive research on this

This magazine article comes complete with illustrations:

Figure 1 In the nanoimprint lithography process (from the top) a wafer is first metallized (a), then coated with photoresist (b). The **imprint stamp** impresses the structure on the photoresist layer and UV exposure cures the resist (c). After demolding (d), the residual layer is etched down (e), and reactive ion etching transfers the structure into the metal layer (f).
http://oemagazine.com/fromTheMagazine/aug05/feature.html

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Note added at 1 hr (2006-10-30 17:07:32 GMT)
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Like old-fashioned vinyl records, opticals disks have the gold master which is used to make the master that is actually used to make the disks:

A standard optical disk measures 4.724 inches (120 mm) in diameter and .0472 inches (1.2 mm) in thickness. It is made from polycarbonate with a reflective layer of aluminum, coated in lacquer. The master optical disk is made from glass. ***Nickel stampers*** are produced from the glass master and used in an injection-molding machine to "press" or produce multiple copies of the optical disk for distribution. If the disk is double-layered, there will be stampers for each layer, after which the two layers must be bonded together. A double-sided disk requires different stampers for each side, in addition to each layer.
http://www.wisegeek.com/what-is-an-optical-disk.htm

Pioneer has developed a technology that could allow it to cram 510G bytes of data onto a disk the size of a DVD, a company representative said.
The technology uses an electron beam **to make templates from which optical disks can be stamped,** Michiko Kadoi, a company spokeswoman, said last week.
While Pioneer has no immediate plans to commercialize the technology, it believes it could be used to make both recordable and read-only disks with more than 100 times the capacity of today's 12-centimeter DVDs.
http://www.networkworld.com/news/2004/1115pionedevel.html

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Note added at 2 days8 hrs (2006-11-02 00:15:49 GMT)
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metallic reflective layer
The plastic disk is not stamped: it is molded. It is the thin reflective layer of metal is that is stamped in CD replication. However, in CD-Rs, dye is added to this metalic reflective layer so that lasers can encode the disk with data instead of stampers pressing the metallic reflective layer.

In preparing my answer, I was considering the steps of the manufacture of the disk, not the subsequent addition of a label. In my opinion, the thin reflective layer is a printable layer. It is just a different printable layer than the one suggested by others.

References:
The Difference between Duplication and Replication
CD Duplication is the method used for quantities under 500. During duplication the CDs are reproduced by individually "burning" each blank CDR.

CD Replication is the method used for quantities over 500. It is a process whereby a mold of the data, called a Glass Master, is made and then "stamped" onto molded, blank media.
CWS offers full color Offset Printing onto Standard Size Blank CDRs. Get professionally printed blank CDRs and burn the content yourself! (Note: these are blank (recordable) CDRs.)
http://www.cdromdvdduplicationreplication.com/cd-duplication...

Pressing Optical Media
Production of optical media can be divided into two stages: producing the stamper (matrix or mother disk) and the subsequent volume production (pressing) of the medium itself. Making the tool is carried out in several stages. In the traditional process, a photosensitive layer of 100-150nm is deposited to an accuracy of 1nm (1nm = 10-9 m) on a glass or nickel substrate. This is then recorded by laser and subsequently metalized by a photochemical process to produce the final stamper. The process takes around two hours and produces a stamper durable enough to make about 40,000 disks. The eventual pre-recorded optical disks, such as music or software CDs, are made by injecting molding polycarbonate using the stamper to impress the data onto the plastic, hence the term stamper. This so called 'blank' is covered with ***a thin layer of reflective aluminium*** with a protective lacquer coating and then pressed again.
http://www.plantautomation.com/Content/news/article.asp?Buck...{A89944BB-9D30-11D3-9A6E-00A0C9C83AFB}
The mass-produced discs of the CD family have the digital information in the form of microscopic pits pressed into a polycarbonate base which is coated with a light reflective layer. This reflective layer is usually of aluminium, but gold and silver are also used. A transparent lacquer is then placed over the reflective surface to protect it. This surface also carries any label information. As the data are impressed, they cannot be altered or rewritten…

There are several types of write-once recordable discs. The format that is becoming the most widely used is the recordable CD (CD-R or CD-WO) which has been available since 1993. Having the same format and storage capacity as the audio CD and the CD-ROM, the CD-R can be played on the appropriate standard CD drives. ****The polycarbonate body of the disc has a dye layer placed on it which is then coated with a metallic reflective layer. The dye layer carries the data in place of the pits of pressed discs.**** When recording, high-intensity laser pulses change the dye shape so optical properties. The low-intensity read laser reads the changes in reflected light as a digital bit stream. Once written, the data cannot be altered. CD writing drives are available on different speed levels. The CD-R is a well established and standardized format. Different standardized software protocols are available for recording Audio CDs and CD-ROMs. The Photo-CD is a CD-R with a proprietary software protocol to record photographs as electronic still images.
http://www.ifla.org/VI/6/dswmedia/en/txt_opti.htm

Duplication vs. Replication
A. Duplication - uses CD-R recorder technology to "burn" data into a pre-manufactured recordable disc. The data is etched into the blank disc by using a CD recorder. This process is not as stable as stamped CDs. XG Media currently offer duplication services for low runs and rush jobs.
Replication by XG Media - is the process of high speed "stamping" your data into an injection molded CD. The process involves multiple steps but is best suited for orders of 500 or more.

What is the difference between a CDR and a CD-ROM?
A. CDRs are recordable write once CDs. They can be recorded or "burned" in equipment readily available at your local computer store or in professional equipment designed to duplicate many at once. They can be screen-printed or laser printed labels can be applied. They are more expensive to produce, but often the only option for smaller quantities or very quick turnaround times.
http://www.xgmedia.com/support_faq.html